使用栈实现队列(1)(Java)


 1 class MyQueue
 2 {
 3     private Stack s1;
 4     private Stack s2;
 5     
 6     public MyQueue(int size)
 7     {
 8         this.s1 = new Stack(size);
 9         this.s2 = new Stack(size);
10     }
11     
12     public boolean isFull()
13     {
14         return s1.isFull();
15     }
16     
17     public boolean isEmpty()
18     {
19         return s1.isEmpty();
20     }
21     
22     //时间复杂度: O(1)
23     public void EnQueue(int k) throws Exception
24     {
25         if(s1.isFull())
26             throw new Exception("Overflow.");
27         else
28             s1.push(k);
29     }
30     
31     //时间复杂度: O(n)
32     public int DeQueue() throws Exception
33     {
34         if(s1.isEmpty())
35             throw new Exception("Underflow.");
36         else
37         {
38             for(int i = this.s1.getLength(); i > 1; i--)
39                 s2.push(s1.pop());
40             int key = s1.pop();
41             while(!s2.isEmpty())
42                 s1.push(s2.pop());
43             return key;
44         }
45     }
46 }
47 
48 class Stack
49 {
50     private int top;
51     private int[] a;
52     
53     public Stack(int size)
54     {
55         this.top = -1;
56         this.a = new int[size];
57     }
58     
59     public boolean isFull()
60     {
61         return this.top == this.a.length - 1;
62     }
63     
64     public boolean isEmpty()
65     {
66         return this.top == -1;
67     }
68     
69     public void push(int k) throws Exception
70     {
71         /*if(this.isFull())
72             throw new Exception("Overflow.");*/
73         //else
74             this.a[++top] = k;
75     }
76     
77     public int pop() throws Exception
78     {
79         /*if(this.isEmpty())
80             throw new Exception("Underflow.");*/
81         //else
82             return this.a[top--];
83     }
84     
85     public int getLength()
86     {
87         return this.top + 1;
88     }
89 }

 


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