【LeetCode】232 - Implement Queue using Stacks

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Implement the following operations of a queue using stacks.

• push(x) -- Push element x to the back of queue.
• pop() -- Removes the element from in front of queue.
• peek() -- Get the front element.
• empty() -- Return whether the queue is empty.

Notes:

• You must use only standard operations of a stack -- which means only push to top, peek/pop from top, size, and is empty operations are valid.
• Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.
• You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).

•  1 class Queue {
   2 public:
   3     // Push element x to the back of queue.
   4     void push(int x) {
   5         stk.push(x);
   6     }
   7 
   8     // Removes the element from in front of queue.
   9     void pop(void) {
  10         stack<int> temp;
  11         while(stk.size()!=1){
  12             int x=stk.top();
  13             stk.pop();
  14             temp.push(x);
  15         }
  16         stk.pop();
  17         while(!temp.empty()){
  18             int x=temp.top();
  19             temp.pop();
  20             stk.push(x);
  21         }
  22     }
  23 
  24     // Get the front element.
  25     int peek(void) {
  26         stack<int> temp;
  27         while(stk.size()!=1){
  28             int x=stk.top();
  29             stk.pop();
  30             temp.push(x);
  31         }
  32         int x=stk.top();
  33         while(!temp.empty()){
  34             int x=temp.top();
  35             temp.pop();
  36             stk.push(x);
  37         }
  38         return x;
  39     }
  40 
  41     // Return whether the queue is empty.
  42     bool empty(void) {
  43         return stk.empty();
  44     }
  45 private:
  46     stack<int> stk;
  47 };

   

【LeetCode】232 - Implement Queue using Stacks

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原文地址：http://www.cnblogs.com/irun/p/4695636.html