【LeetCode 225_数据结构_栈_实现】Implement Stack using Queues

 class Stack {
 public:
     // Push element x onto stack.
     void push(int x) {
         int len = nums.size();
         nums.push(x);
         for (int i = ; i < len; ++i) {
             nums.push(nums.front());
             nums.pop();
         }
     }

     // Removes the element on top of the stack.
     void pop() {
         nums.pop();
     }

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

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