1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
|
/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2006, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
// $Id$
package scala;
import Predef._;
import scala.collection.mutable.ListBuffer;
/** This object provides methods for creating specialized lists, and for
* transforming special kinds of lists (e.g. lists of lists).
*
* @author Martin Odersky and others
* @version 1.0, 15/07/2003
*/
object List {
/** Create a list with given elements.
*
* @param xs the elements to put in the list
* @return the list containing elements xs.
*/
def apply[A](xs: A*): List[A] =
// TODO: remove the type test once nsc becomes standard
if (xs.isInstanceOf$erased[List[A]])
xs.asInstanceOf$erased[List[A]];
else
fromArray(xs.asInstanceOf$erased[Array[A]]);
/** Create a sorted list of all integers in a range.
*
* @param from the start value of the list
* @param end the end value of the list
* @return the sorted list of all integers in range [from;end).
*/
def range(from: Int, end: Int): List[Int] =
range(from, end, 1);
/** Create a sorted list of all integers in a range.
*
* @param from the start value of the list
* @param end the end value of the list
* @param step the increment value of the list
* @return the sorted list of all integers in range [from;end).
*/
def range(from: Int, end: Int, step: Int): List[Int] = {
val b = new ListBuffer[Int]
var i = from
while (i < end) {
b += i
i = i + step
}
b.toList
}
/** Create a sorted list of all integers in a range.
*
* @param from the start value of the list
* @param end the end value of the list
* @param step the increment function of the list
* @return the sorted list of all integers in range [from;end).
*/
def range(from: Int, end: Int, step: Int => Int): List[Int] = {
val b = new ListBuffer[Int]
var i = from
while (i < end) {
b += i
i = i + step(i)
}
b.toList
}
/** Create a list containing several copies of an element.
*
* @param n the length of the resulting list
* @param elem the element composing the resulting list
* @return a list composed of n elements all equal to elem
*/
def make[a](n: Int, elem: a): List[a] = {
val b = new ListBuffer[a]
var i = 0
while (i < n) {
b += elem
i = i + 1
}
b.toList
}
/** Create a list by applying a function to successive integers.
*
* @param n the length of the resulting list
* @param maker the procedure which, given an integer n, returns the
* nth element of the resulting list, where n is in [0;n).
* @return the list obtained by applying the maker function to successive
* integers from 0 to n (exclusive).
*/
def tabulate[a](n: Int, maker: Int => a): List[a] = {
val b = new ListBuffer[a]
var i = 0
while (i < n) {
b += maker(i)
i = i + 1
}
b.toList
}
/** Concatenate all the elements of a given list of lists.
* @param l the list of lists that are to be concatenated
* @return the concatenation of all the lists
*/
def flatten[a](l: List[List[a]]): List[a] = {
val b = new ListBuffer[a]
var xsc = l
while (!xsc.isEmpty) {
var xc = xsc.head
while (!xc.isEmpty) {
b += xc.head
xc = xc.tail
}
xsc = xsc.tail
}
b.toList
}
/** Transforms a list of pair into a pair of lists.
*
* @param l the list of pairs to unzip
* @return a pair of lists: the first list in the pair contains the list
*/
def unzip[a,b](l: List[Pair[a,b]]): Pair[List[a], List[b]] = {
val b1 = new ListBuffer[a]
val b2 = new ListBuffer[b]
var xc = l
while (!xc.isEmpty) {
b1 += xc.head._1
b2 += xc.head._2
xc = xc.tail
}
Pair(b1.toList, b2.toList)
}
/** Converts an iterator to a list
*
* @param it the iterator to convert
* @return a list that contains the elements returned by successive
* calls to <code>it.next</code>
*/
def fromIterator[a](it: Iterator[a]): List[a] = {
val b = new ListBuffer[a]
while (it.hasNext) b += it.next
b.toList
}
/** Converts an array into a list.
*
* @param arr the array to convert
* @return a list that contains the same elements than <code>arr</code>
* in the same order
*/
def fromArray[a](arr: Array[a]): List[a] = fromArray(arr, 0, arr.length);
/** Converts a range of an array into a list.
*
* @param arr the array to convert
* @param start the first index to consider
* @param len the lenght of the range to convert
* @return a list that contains the same elements than <code>arr</code>
* in the same order
*/
def fromArray[a](arr: Array[a], start: Int, len: Int): List[a] = {
var res: List[a] = Nil;
var i = start + len;
while (i > start) {
i = i - 1;
res = arr(i) :: res;
}
res
}
/** Parses a string which contains substrings separated by a
*
* separator character and returns a list of all substrings.
* @param str the string to parse
* @param separator the separator character
* @return the list of substrings
*/
def fromString(str: String, separator: Char): List[String] = {
var words: List[String] = List();
var pos = str.length();
while (pos > 0) {
val pos1 = str.lastIndexOf(separator, pos - 1);
if (pos1 + 1 < pos)
words = str.substring(pos1 + 1, pos) :: words;
pos = pos1
}
words
}
/** Returns the given string as a list of characters.
*
* @param str the string to convert.
* @return the string as a list of characters.
*/
def fromString(str: String): List[Char] = {
var res: List[Char] = Nil;
var i = str.length();
while (i > 0) {
i = i - 1;
res = str.charAt(i) :: res;
}
res
}
/** Returns the given list of characters as a string.
*
* @param xs the list to convert.
* @return the list in form of a string.
*/
def toString(xs: List[Char]): String = {
val sb = new StringBuffer();
var xc = xs;
while (!xc.isEmpty) {
sb.append(xc.head);
xc = xc.tail;
}
sb.toString()
}
/** Like xs map f, but returns xs unchanged if function `f' maps all elements to themselves
*/
def mapConserve[a <: AnyRef](xs: List[a])(f: a => a): List[a] = {
def loop(ys: List[a]): List[a] =
if (ys.isEmpty) xs
else {
val head0 = ys.head
val head1 = f(head0)
if (head1 eq head0) {
loop(ys.tail)
} else {
val ys1 = head1 :: mapConserve(ys.tail)(f)
if (xs eq ys) ys1
else {
val b = new ListBuffer[a]
var xc = xs
while (xc ne ys) {
b += xc.head
xc = xc.tail
}
b.prependToList(ys1)
}
}
}
loop(xs)
}
/** Returns the list resulting from applying the given function <code>f</code> to
* corresponding elements of the argument lists.
*
* @param f function to apply to each pair of elements.
* @return <code>[f(a0,b0), ..., f(an,bn)]</code> if the lists are
* <code>[a0, ..., ak]</code>, <code>[b0, ..., bl]</code> and
* <code>n = min(k,l)</code>
*/
def map2[a,b,c](xs: List[a], ys: List[b])(f: (a, b) => c): List[c] = {
val b = new ListBuffer[c]
var xc = xs
var yc = ys
while (!xc.isEmpty && !yc.isEmpty) {
b += f(xc.head, yc.head)
xc = xc.tail
yc = yc.tail
}
b.toList
}
/** Returns the list resulting from applying the given function <code>f</code> to
* corresponding elements of the argument lists.
*
* @param f function to apply to each pair of elements.
* @return <code>[f(a0,b0,c0), ..., f(an,bn,cn)]</code> if the lists are
* <code>[a0, ..., ak]</code>, <code>[b0, ..., bl]</code>, <code>[c0, ..., cm]</code> and
* <code>n = min(k,l,m)</code>
*/
def map3[a,b,c, d](xs: List[a], ys: List[b], zs: List[c])(f: (a, b, c) => d): List[d] = {
val b = new ListBuffer[d]
var xc = xs
var yc = ys
var zc = zs
while (!xc.isEmpty && !yc.isEmpty && !zc.isEmpty) {
b += f(xc.head, yc.head, zc.head)
xc = xc.tail
yc = yc.tail
zc = zc.tail
}
b.toList
}
/** Tests whether the given predicate <code>p</code> holds
* for all corresponding elements of the argument lists.
*
* @param p function to apply to each pair of elements.
* @return <code>n == 0 || (p(a0,b0) && ... && p(an,bn))]</code> if the lists are
* <code>[a0, ..., ak]</code>, <code>[b0, ..., bl]</code> and
* <code>m = min(k,l)</code>
*/
def forall2[a,b](xs: List[a], ys: List[b])(f: (a, b) => boolean): boolean = {
var xc = xs
var yc = ys
while (!xc.isEmpty && !yc.isEmpty) {
if (!f(xc.head, yc.head)) return false
xc = xc.tail
yc = yc.tail
}
true
}
/** Tests whether the given predicate <code>p</code> holds
* for some corresponding elements of the argument lists.
*
* @param p function to apply to each pair of elements.
* @return <code>n != 0 && (p(a0,b0) || ... || p(an,bn))]</code> if the lists are
* <code>[a0, ..., ak]</code>, <code>[b0, ..., bl]</code> and
* <code>m = min(k,l)</code>
*/
def exists2[a,b](xs: List[a], ys: List[b])(f: (a, b) => boolean): boolean = {
var xc = xs
var yc = ys
while (!xc.isEmpty && !yc.isEmpty) {
if (f(xc.head, yc.head)) return true
xc = xc.tail
yc = yc.tail
}
false
}
/** Transposes a list of lists.
* pre: All element lists have the same length.
*/
def transpose[a](xss: List[List[a]]): List[List[a]] =
if (xss.head.isEmpty) List()
else (xss map (xs => xs.head)) :: transpose(xss map (xs => xs.tail));
/** Lists with ordered elements are ordered
*/
implicit def list2ordered[a <% Ordered[a]](x: List[a]): Ordered[List[a]] = new Ordered[List[a]] {
def compareTo [b >: List[a] <% Ordered[b]](y: b): Int = y match {
case y1: List[a] => compareLists(x, y1);
case _ => -(y compareTo x)
}
private def compareLists(xs: List[a], ys: List[a]): Int = {
if (xs.isEmpty && ys.isEmpty) 0
else if (xs.isEmpty) -1
else if (ys.isEmpty) 1
else {
val s = xs.head compareTo ys.head;
if (s != 0) s
else compareLists(xs.tail, ys.tail)
}
}
}
def view[a <% Ordered[a]](x: List[a]): Ordered[List[a]] = list2ordered(x);
}
/** A class representing an ordered collection of elements of type
* <code>a</code>. This class comes with two implementing case
* classes <code>scala.Nil</code> and <code>scala.::</code> that
* implement the abstract members <code>isEmpty</code>,
* <code>head</code> and <code>tail</code>.
*
* @author Martin Odersky and others
* @version 1.0, 16/07/2003
*/
sealed abstract class List[+a] extends Seq[a] {
/** Returns true if the list does not contain any elements.
* @return true, iff the list is empty.
*/
def isEmpty: Boolean;
/** Returns this first element of the list.
* @return the first element of this list.
* @throws <code>java.lang.RuntimeException</code> if the list is empty.
*/
def head: a;
/** Returns this list without its first element.
* @return this list without its first element.
* @throws <code>java.lang.RuntimeException</code> if the list is empty.
*/
def tail: List[a];
/** Add an element <code>x</code> at the beginning of this list.
* <p/>
* Ex:<br/>
* <code>1 :: [2, 3] = [2, 3].::(1) = [1, 2, 3]</code>.
* @param x the element to append.
* @return the list with <code>x</code> appended at the beginning.
*/
def ::[b >: a] (x: b): List[b] =
new scala.::(x, this);
/** Returns a list resulting from the concatenation of the given
* list <code>prefix</code> and this list.
* <p/>
* Ex:<br/>
* <code>[1, 2] ::: [3, 4] = [3, 4].:::([1, 2]) = [1, 2, 3, 4]</code>.
* @param prefix the list to concatenate at the beginning of this list.
* @return the concatenation of the two lists.
*/
def :::[b >: a](prefix: List[b]): List[b] =
if (isEmpty) prefix
else {
val b = new ListBuffer[b]
var those = prefix
while (!those.isEmpty) {
b += those.head
those = those.tail
}
b.prependToList(this)
}
/** Reverse the given prefix and append the current list to that.
* This function is equivalent to an application of <code>reverse</code>
* on the prefix followed by a call to <code>:::</code>, but more
* efficient (and tail recursive).
* @param prefix the prefix to reverse and then prepend
* @return the concatenation of the reversed prefix and the current list.
*/
def reverse_:::[b >: a](prefix: List[b]): List[b] = prefix match {
case Nil => this
case head :: tail => tail.reverse_:::(head :: this)
}
/** Returns the number of elements in the list.
*
* @return the number of elements in the list.
*/
def length: Int = {
var these = this;
var len = 0;
while (!these.isEmpty) {
len = len + 1;
these = these.tail
}
len
}
/** Creates a list with all indices in the list. This is
* equivalent to a call to <code>List.range(0, xs.length)</code>.
*
* @return a list of all indices in the list.
*/
def indices: List[Int] = {
val b = new ListBuffer[Int]
var i = 0
var these = this
while (!these.isEmpty) {
b += i
i = i + 1
these = these.tail
}
b.toList
}
/** Returns the elements in the list as an iterator
*
* @return an iterator on the list elements.
*/
def elements: Iterator[a] = new Iterator[a] {
var these = List.this;
def hasNext: Boolean = !these.isEmpty;
def next: a =
if (!hasNext)
error("next on empty Iterator")
else {
val result = these.head; these = these.tail; result
}
}
/** Transform this sequence into a list of all elements.
*
* @return a list which enumerates all elements of this sequence.
*/
//override def toList: List[a] = this; //!!!
/** Returns the list without its last element.
*
* @return the list without its last element.
* @throws <code>java.lang.RuntimeException</code> if the list is empty.
*/
def init: List[a] =
if (isEmpty) error("Nil.init")
else {
val b = new ListBuffer[a]
var elem = head
var next = tail
while (!next.isEmpty) {
b += elem
elem = next.head
next = next.tail
}
b.toList
}
/** Returns the last element of this list.
*
* @return the last element of the list.
* @throws <code>java.lang.RuntimeException</code> if the list is empty.
*/
def last: a =
if (isEmpty) error("Nil.last")
else if (tail.isEmpty) head
else tail.last;
/** Returns the <code>n</code> first elements of this list.
*
* @param n the number of elements to take.
* @return the <code>n</code> first elements of this list.
*/
override def take(n: Int): List[a] = {
val b = new ListBuffer[a]
var i = 0
var these = this
while (!these.isEmpty && i < n) {
i = i + 1
b += these.head
these = these.tail
}
b.toList
}
/** Returns the list without its <code>n</code> first elements.
*
* @param n the number of elements to drop.
* @return the list without its <code>n</code> first elements.
*/
override def drop(n: Int): List[a] =
if (n == 0 || isEmpty) this
else (tail drop (n-1));
/** Returns the rightmost <code>n</code> elements from this list.
*
* @param n the number of elements to take
* @return the suffix of length <code>n</code> of the list
* @throws <code>java.lang.RuntimeException</code> if the list is too short.
*/
def takeRight(n: Int): List[a] = {
def loop(lead: List[a], lag: List[a]): List[a] = lead match {
case Nil => lag
case _ :: tail => loop(tail, lag.tail)
}
loop(drop(n), this)
}
/** Returns the list wihout its rightmost <code>n</code> elements.
*
* @param n the number of elements to take
* @return the suffix of length <code>n</code> of the list
* @throws <code>java.lang.RuntimeException</code> if the list is too short.
*/
def dropRight(n: Int): List[a] = {
def loop(lead: List[a], lag: List[a]): List[a] = lead match {
case Nil => Nil
case _ :: tail => lag.head :: loop(tail, lag.tail)
}
loop(drop(n), this)
}
/** Split the list at a given point and return the two parts thus
* created.
*
* @param n the position at which to split
* @return a pair of lists composed of the first <code>n</code>
* elements, and the other elements.
*/
def splitAt(n: Int): Pair[List[a], List[a]] = {
val b = new ListBuffer[a]
var i = 0
var these = this;
while (!these.isEmpty && i < n) {
i = i + 1
b += these.head
these = these.tail
}
Pair(b.toList, these)
}
/** Returns the longest prefix of this list whose elements satisfy
* the predicate <code>p</code>.
*
* @param p the test predicate.
* @return the longest prefix of this list whose elements satisfy
* the predicate <code>p</code>.
*/
def takeWhile(p: a => Boolean): List[a] = {
val b = new ListBuffer[a]
var these = this
while (!these.isEmpty && p(these.head)) {
b += these.head
these = these.tail
}
b.toList
}
/** Returns the longest suffix of this list whose first element
* does not satisfy the predicate <code>p</code>.
*
* @param p the test predicate.
* @return the longest suffix of the list whose first element
* does not satisfy the predicate <code>p</code>.
*/
def dropWhile(p: a => Boolean): List[a] =
if (isEmpty || !p(head)) this
else tail dropWhile p;
/** Returns the longest prefix of the list whose elements all satisfy
* the given predicate, and the rest of the list.
*
* @param p the test predicate
* @return a pair consisting of the longest prefix of the list whose
* elements all satisfy <code>p</code>, and the rest of the list.
*/
def span(p: a => Boolean): Pair[List[a], List[a]] = {
val b = new ListBuffer[a]
var these = this
while (!these.isEmpty && p(these.head)) {
b += these.head
these = these.tail
}
Pair(b.toList, these)
}
/** Like <code>span</code> but with the predicate inverted.
*/
def break(p: a => Boolean): Pair[List[a], List[a]] = span { x => !p(x) }
/** Returns the <code>n</code>-th element of this list. The first element
* (head of the list) is at position 0.
*
* @param n index of the element to return
* @return the element at position <code>n</code> in this list.
* @throws <code>java.lang.RuntimeException</code> if the list is too short.
*/
def apply(n: Int): a = drop(n).head;
/** Returns the list resulting from applying the given function <code>f</code> to each
* element of this list.
*
* @param f function to apply to each element.
* @return <code>[f(a0), ..., f(an)]</code> if this list is <code>[a0, ..., an]</code>.
*/
def map[b](f: a => b): List[b] = {
val b = new ListBuffer[b]
var these = this
while (!these.isEmpty) {
b += f(these.head)
these = these.tail
}
b.toList
}
/** Apply a function to all the elements of the list, and return the
* reversed list of results. This is equivalent to a call to <code>map</code>
* followed by a call to <code>reverse</code>, but more efficient.
*
* @param f the function to apply to each elements.
* @return the reversed list of results.
*/
def reverseMap[b](f: a => b): List[b] = {
def loop(l: List[a], res: List[b]): List[b] = l match {
case Nil => res
case head :: tail => loop(tail, f(head) :: res)
}
loop(this, Nil)
}
/** Apply the given function <code>f</code> to each element of this list
* (while respecting the order of the elements).
*
* @param f the treatment to apply to each element.
*/
override def foreach(f: a => Unit): Unit = {
var these = this;
while (!these.isEmpty) {
f(these.head)
these = these.tail
}
}
/** Returns all the elements of this list that satisfy the
* predicate <code>p</code>. The order of the elements is preserved.
*
* @param p the redicate used to filter the list.
* @return the elements of this list satisfying <code>p</code>.
*/
def filter(p: a => Boolean): List[a] = {
// return same list if all elements satisfy p
var these = this
while (!these.isEmpty && p(these.head)) {
these = these.tail
}
if (these.isEmpty) this
else {
val b = new ListBuffer[a]
var these1 = this;
while (these1 ne these) {
b += these1.head
these1 = these1.tail
}
while (!these.isEmpty) {
if (p(these.head)) b += these.head
these = these.tail
}
b.toList
}
}
/** Removes all elements of the list which satisfy the predicate
* <code>p</code>. This is like <code>filter</code> with the
* predicate inversed.
*
* @param p the predicate to use to test elements
* @return the list without all elements which satisfy <code>p</code>
*/
def remove(p: a => Boolean): List[a] = filter (x => !p(x));
/** Partition the list in two sub-lists according to a predicate.
*
* @param p the predicate on which to partition
* @return a pair of lists: the list of all elements which satisfy
* <code>p</code> and the list of all elements which do not. The
* relative order of the elements in the sub-lists is the same as in
* the original list.
*/
def partition(p: a => Boolean): Pair[List[a], List[a]] = {
val btrue = new ListBuffer[a]
val bfalse = new ListBuffer[a]
var these = this
while (!these.isEmpty) {
(if (p(these.head)) btrue else bfalse) += these.head
these = these.tail
}
Pair(btrue.toList, bfalse.toList)
}
/** Sort the list according to the comparison function
* <code><(e1: a, e2: a) => Boolean</code>,
* which should be true iff e1 is smaller than e2.
* Note: The current implementation is inefficent for
* already sorted lists.
*
* @param lt the comparison function
* @return a list sorted according to the comparison function
* <code><(e1: a, e2: a) => Boolean</code>.
*/
def sort(lt : (a,a) => Boolean): List[a] = {
def sort_1(smaller: List[a], acc: List[a]): List[a] =
smaller match {
case Nil =>
acc
case List(x) =>
x::acc
case List(x, y) =>
if (lt(x, y)) x::(y::acc) else y::x::acc
case List(x, y, z) =>
if (lt(x, y)) {
if (lt(y, z)) x::y::z::acc
else if (lt(x, z)) x::z::y::acc
else z::x::y::acc
} else if (lt(x, z)) y::x::z::acc
else if (lt(z, y)) z::y::x::acc
else y::z::x::acc
case hd1::hd2::hd3::tail => {
val List(x, y, z) = sort_1(hd1::hd2::hd3::Nil, Nil);
val Pair(small, large) = tail.partition((e2) => lt(e2, y));
sort_1(x::small, y::sort_1(z::large, acc))
}
}
this match {
case Nil =>
this
case List(x) =>
this
case List(x, y) =>
if (lt(x, y)) this else y::x::Nil
case List(x, y, z) =>
if (lt(x, y)) {
if (lt(y, z)) this
else if (lt(x, z)) x::z::y::Nil
else z::x::y::Nil
} else if (lt(x, z)) y::x::z::Nil
else if (lt(z, y)) z::y::x::Nil
else y::z::x::Nil
case hd1::hd2::hd3::tail => {
val List(x, y, z) = sort_1(hd1::hd2::hd3::Nil, Nil);
val Pair(small,large) = tail.partition((e2) => lt(e2, y));
sort_1(x::small, y::sort_1(z::large, Nil));
}
}
}
/** Count the number of elements in the list which satisfy a predicate.
*
* @param p the predicate for which to count
* @return the number of elements satisfying the predicate <code>p</code>.
*/
def count(p: a => Boolean): Int = {
var cnt = 0
var these = this
while (!these.isEmpty) {
if (p(these.head)) cnt = cnt + 1
these = these.tail
}
cnt
}
/** Tests if the predicate <code>p</code> is satisfied by all elements
* in this list.
*
* @param p the test predicate.
* @return True iff all elements of this list satisfy the predicate <code>p</code>.
*/
override def forall(p: a => Boolean): Boolean = {
var these = this
while (!these.isEmpty) {
if (!p(these.head)) return false
these = these.tail
}
true
}
/** Tests the existence in this list of an element that satisfies the predicate
* <code>p</code>.
*
* @param p the test predicate.
* @return true iff there exists an element in this list that satisfies
* the predicate <code>p</code>.
*/
override def exists(p: a => Boolean): Boolean = {
var these = this
while (!these.isEmpty) {
if (p(these.head)) return true
these = these.tail
}
false
}
/** Tests if the given value <code>elem</code> is a member of this
* iterable object.
*
* @param elem element whose membership has to be tested.
* @return True iff there is an element of this list which is
* equal (w.r.t. <code>==</code>) to <code>elem</code>.
*/
def contains(elem: Any): boolean = exists (.==(elem))
/** Find and return the first element of the list satisfying a
* predicate, if any.
*
* @param p the predicate
* @return the first element in the list satisfying <code>p</code>,
* or <code>None</code> if none exists.
*/
override def find(p: a => Boolean): Option[a] = {
var these = this
while (!these.isEmpty) {
if (p(these.head)) return Some(these.head)
these = these.tail
}
None
}
/** Combines the elements of this list together using the binary
* operator <code>op</code>, from left to right, and starting with
* the value <code>z</code>.
*
* @return <code>op(... (op(op(z,a0),a1) ...), an)</code> if the list
* is <code>[a0, a1, ..., an]</code>.
*/
override def foldLeft[b](z: b)(f: (b, a) => b): b = {
var acc = z
var these = this
while (!these.isEmpty) {
acc = f(acc, these.head)
these = these.tail
}
acc
}
/** Combines the elements of this list together using the binary
* operator <code>op</code>, from rigth to left, and starting with
* the value <code>z</code>.
*
* @return <code>a0 op (... op (an op z)...)</code> if the list
* is <code>[a0, a1, ..., an]</code>.
*/
override def foldRight[b](z: b)(f: (a, b) => b): b = this match {
case Nil => z
case x :: xs => f(x, xs.foldRight(z)(f))
}
def reduceLeft[b >: a](f: (b, b) => b): b = this match {
case Nil => error("Nil.reduceLeft")
case x :: xs => ((xs: List[b]) foldLeft (x: b))(f)
}
def reduceRight[b >: a](f: (b, b) => b): b = this match {
case Nil => error("Nil.reduceRight")
case x :: Nil => x: b
case x :: xs => f(x, xs reduceRight f)
}
/** Applies the given function <code>f</code> to each element of
* this list, then concatenates the results.
*
* @param f the function to apply on each element.
* @return <code>f(a0) ::: ... ::: f(an)</code> if this list is
* <code>[a0, ..., an]</code>.
*/
def flatMap[b](f: a => List[b]): List[b] = {
val b = new ListBuffer[b]
var these = this
while (!these.isEmpty) {
var those = f(these.head)
while (!those.isEmpty) {
b += those.head
those = those.tail
}
these = these.tail
}
b.toList
}
/** Reverses the elements of this list.
* <p/>
* Ex: <br/>
* <code>[1, 2, 3] reverse = [3, 2, 1]</code>.
*
* @return the elements of this list in reverse order.
*/
def reverse: List[a] =
foldLeft(Nil : List[a])((xs, x) => x :: xs);
/** Returns a string representation of this list. The resulting string
* begins with the string <code>start</code> and is finished by the string
* <code>end</code>. Inside, the string representations of elements (w.r.t.
* the method <code>toString()</code>) are separated by the string
* <code>sep</code>.
* <p/>
* Ex: <br/>
* <code>List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"</code>
*
* @param start starting string.
* @param sep separator string.
* @param end ending string.
* @return a string representation of this list.
*/
def mkString(start: String, sep: String, end: String): String = this match {
case Nil => start + end
case last :: Nil => start + last + end
case fst :: tail => start + fst + sep + tail.mkString("", sep, end)
}
override def toString() = mkString("List(", ",", ")");
/** Returns a list formed from this list and the specified list
* <code>that</code> by associating each element of the former with
* the element at the same position in the latter.
*
* @param <code>that</code> must have the same length as the self list.
* @return <code>[(a0,b0), ..., (an,bn)]</code> when
* <code>[a0, ..., an] zip [b0, ..., bn]</code> is invoked.
*/
def zip[b](that: List[b]): List[Pair[a,b]] = {
val b = new ListBuffer[Pair[a, b]]
var these = this
var those = that
while (!these.isEmpty && !those.isEmpty) {
b += Pair(these.head, those.head)
these = these.tail
those = those.tail
}
b.toList
}
/** Returns a list formed from this list and the specified list
* <code>that</code> by associating each element of the former with
* the element at the same position in the latter.
*
* @param <code>that</code> may have a different length as the self list.
* @param <code>thisElem</code> is used to fill up the resulting list if
* the self list is shorter than <code>that</code>
* @param <code>thatElem</code> is used to fill up the resulting list if
* <code>that</code> is shorter than the self list
* @return <code>[(a0,b0), ..., (an,bn), (elem,bn+1), ..., (elem,bm)]</code>
* when <code>[a0, ..., an] zip [b0, ..., bm]</code> is invoked where
* <code>m > n</code>.
*/
def zipAll[b, c >: a, d >: b](that: List[b], thisElem: c, thatElem: d): List[Pair[c,d]] = {
val b = new ListBuffer[Pair[c, d]]
var these = this
var those = that
while (!these.isEmpty && !those.isEmpty) {
b += Pair(these.head, those.head)
these = these.tail
those = those.tail
}
while (!these.isEmpty) {
b += Pair(these.head, thatElem)
these = these.tail
}
while (!those.isEmpty) {
b += Pair(thisElem, those.head)
those = those.tail
}
b.toList
}
/** Computes the union of this list and the given list
* <code>that</code>.
*
* @param that the list of elements to add to the list.
* @return a list without doubles containing the elements of this
* list and those of the given list <code>that</code>.
*/
def union[b >: a](that: List[b]): List[b] = {
val b = new ListBuffer[b]
var these = this
while (!these.isEmpty) {
if (!that.contains(these.head)) b += these.head
these = these.tail
}
b.prependToList(that)
}
/** Computes the difference between this list and the given list
* <code>that</code>.
*
* @param that the list of elements to remove from this list.
* @return this list without the elements of the given list <code>that</code>.
*/
def diff[b >: a](that: List[b]): List[b] = {
val b = new ListBuffer[b]
var these = this
while (!these.isEmpty) {
if (!that.contains(these.head)) b += these.head
these = these.tail
}
b.toList
}
/** Computes the intersection between this list and the given list
* <code>that</code>.
*
* @param that the list to intersect.
* @return the list of elements contained both in this list and
* in the given list <code>that</code>.
*/
def intersect[b >: a](that: List[b]): List[b] = filter(x => that contains x);
/** Removes redundant elements from the list. Uses the method <code>==</code>
* to decide if two elements are identical.
*
* @return the list without doubles.
*/
def removeDuplicates: List[a] = {
val b = new ListBuffer[a]
var these = this
while (!these.isEmpty) {
if (!these.tail.contains(these.head)) b += these.head
these = these.tail
}
b.toList
}
}
/** The empty list.
*
* @author Martin Odersky
* @version 1.0, 15/07/2003
*/
[SerialVersionUID(0 - 8256821097970055419L)]
case object Nil extends List[All] {
def isEmpty = true;
def head: All = error("head of empty list");
def tail: List[All] = error("tail of empty list");
}
/** A non empty list characterized by a head and a tail.
*
* @author Martin Odersky
* @version 1.0, 15/07/2003
*/
[SerialVersionUID(0L - 8476791151983527571L)]
final case class ::[b](hd: b, /*private[scala]*/ var tl: List[b]) extends List[b] {
def head = hd;
def tail = tl;
def isEmpty: boolean = false;
}
|