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
|
package scala.collection.mutable;
private object Utils{
def growArray(x : Array[AnyRef]) = {
val y = new Array[AnyRef](x.length * 2);
Array.copy(x, 0, y, 0, x.length);
y;
}
def clone(x : Array[AnyRef]) = {
val y = new Array[AnyRef](x.length);
Array.copy(x, 0, y, 0, x.length);
y;
}
}
/**
* Simple stack class backed by an array. Should be significantly faster
* than the standard mutable stack.
*/
class ArrayStack[T] private(private var table : Array[AnyRef],
private var index : Int) extends Collection[T]{
def this() = this(new Array[AnyRef](1), 0);
/**
* Push an element onto the stack.
*
* @param x The element to push
*/
def push(x : T) = {
if (index == table.length) table = Utils.growArray(table);
table(index) = x.asInstanceOf[AnyRef];
index += 1;
}
/**
* Pop the top element off the stack.
*/
def pop = {
if (index == 0) error("Stack empty");
index -= 1;
val x = table(index).asInstanceOf[T];
table(index) = null;
x;
}
/**
* View the top element of the stack.
*/
def peek = table(index - 1).asInstanceOf[T]
/**
* Duplicate the top element of the stack.
*/
def dup = push(peek);
/**
* Empties the stack.
*/
def clear = {
index = 0;
table = new Array(1);
}
/**
* Empties the stack, passing all elements on it in FIFO order to the
* provided function.
*
* @param f The function to drain to.
*/
def drain(f : T => Unit) = while(!isEmpty) f(pop);
/**
* Pushes all the provided elements onto the stack.
*
* @param x The source of elements to push
*/
def ++=(x : Iterable[T]) = x.foreach(this +=(_))
/**
* Pushes all the provided elements onto the stack.
*
* @param x The source of elements to push
*/
def ++=(x : Iterator[T]) = x.foreach(this +=(_))
/**
* Alias for push.
*
* @param x The element to push
*/
def +=(x : T) = push(x);
/**
* Pop the top two elements off the stack, apply f to them and push the result
* back on to the stack.
*
* @param f The combining function
*/
def combine(f : (T, T) => T) = push(f(pop, pop));
/**
* Repeatedly combine the top elements of the stack until the stack contains only
* one element.
*/
def reduceWith(f : (T, T) => T) = while(size > 1) combine(f)
def size = index;
/**
* Evaluates the expression, preserving the contents of the stack so that
* any changes the evaluation makes to the stack contents will be undone after
* it completes.
*
* @param action The action to run.
*/
def preserving[T](action : => T) = {
val oldIndex = index;
val oldTable = Utils.clone(table);
try{
action;
} finally {
index = oldIndex;
table = oldTable;
}
}
override def isEmpty = index == 0;
/**
* Iterates over the stack in fifo order.
*/
def elements = new Iterator[T]{
var currentIndex = index;
def hasNext = currentIndex > 0;
def next = {
currentIndex -= 1;
table(currentIndex).asInstanceOf[T];
}
}
override def foreach(f : T => Unit){
var currentIndex = index;
while(currentIndex > 0){
currentIndex -= 1;
f(table(currentIndex).asInstanceOf[T]);
}
}
override def clone = new ArrayStack[T](Utils.clone(table), index);
}
|