Implement Stack by Two Queues (Ladder)

Description

Implement a stack by two queues. The queue is first in first out (FIFO). That means you can not directly pop the last element in a queue.

Example

push(1)
pop()
push(2)
isEmpty() // return false
top() // return 2
pop()
isEmpty() // return true

Link

Lintcode_ladder

Method

1. x
2. x

Example

1. 1

   class Stack {
   public:
    void Movedata() {
        while (q1.size() > 1) {
            int tmp = q1.front();
            q1.pop();
            q2.push(tmp);
        }
        return;
    }
    void swapqueue () {
        queue<int> tmp(q1);
        q1 = q2;
        q2 = tmp;
        return;
    }
    // Push a new item into the stack
    void push(int x) {
        // Write your code here
        q1.push(x);
        return;
    }
    // Pop the top of the stack
    void pop() {
        // Write your code here
        Movedata();
        q1.pop();
        swapqueue();
        return;
    }
    // Return the top of the stack
    int top() {
        // Write your code here
        Movedata();
        int result = q1.front();
        q1.pop();
        q2.push(result);
        swapqueue();
        return result;
    }
    // Check the stack is empty or not.
    bool isEmpty() {
        // Write your code here
        return q1.empty();
    }
    queue<int> q1;
    queue<int> q2;
   };
   

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