232 - Implement Queue Using Stacks

#easy

Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (push, peek, pop, and empty).

Implement the MyQueue class:

• void push(int x) Pushes element x to the back of the queue.
• int pop() Removes the element from the front of the queue and returns it.
• int peek() Returns the element at the front of the queue.
• boolean empty() Returns true if the queue is empty, false otherwise.

class MyQueue {
public:
    stack<int> stack_in;
    stack<int> stack_out;
    MyQueue() {
        
    }
    
    void push(int x) {
        stack_in.push(x);
    }
    
    int pop() {
        if ( stack_out.empty() ) {
            while ( !stack_in.empty() ) {
                stack_out.push(stack_in.top());
                stack_in.pop();
            }
        }
 
        int result = stack_out.top();
        stack_out.pop();
        return result;
    }
    
    int peek() {
        int result = pop();
        stack_out.push(result);
        return result;
    }
    
    bool empty() {
        return (stack_in.empty() && stack_out.empty());
    }
};

/**
 * Your MyQueue object will be instantiated and called as such:
 * MyQueue* obj = new MyQueue();
 * obj->push(x);
 * int param_2 = obj->pop();
 * int param_3 = obj->peek();
 * bool param_4 = obj->empty();
 */