232. implement queue using stacks

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).

class Queue {
public:
    stack<int> sIn;
    stack<int> sOut;
    
    void (int x) {
        sIn.push(x);
    }

    // Removes the element from in front of queue.
    void pop(void) {
        if (sOut.empty() && !sIn.empty()) {
            while (!sIn.empty()) {
                sOut.push(sIn.top());
                sIn.pop();
            }
        }
        
        sOut.pop();
    }

    // Get the front element.
    int peek(void) {
        if (sOut.empty() && !sIn.empty()) {
            while (!sIn.empty()) {
                sOut.push(sIn.top());
                sIn.pop();
            }
        }
        
        return sOut.top();
    }

    // Return whether the queue is empty.
    bool empty(void) {
        return sOut.empty() && sIn.empty();
    }
};

232. implement queue using stacks

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