【LeetCode 232_数据结构_队列_实现】Implement Queue using Stacks

 class Queue {
 public:
     // Push element x to the back of queue.
     void push(int x) {
         while (!nums.empty()) {
             nums_assist.push(nums.top());
             nums.pop();
         }
         nums.push(x);
         while (!nums_assist.empty()) {
             nums.push(nums_assist.top());
             nums_assist.pop();
         }
     }

     // Removes the element from in front of queue.
     void pop(void) {
         nums.pop();
     }

     // Get the front element.
     int peek(void) {
         return nums.top();
     }

     // Return whether the queue is empty.
     bool empty(void) {
         return nums.empty();
     }
 private:
     stack<int> nums, nums_assist;
 };