Leetcode 232. Implement Queue using Stacks

難易度

Easy

アプローチ

Stack

class MyQueue {

    public  Stack<Integer> mainStack;
    public  Stack<Integer> subStack;

    public MyQueue() {
        mainStack = new Stack<>();
        subStack = new Stack<>();

    }

    public void push(int x) {
        mainStack.add(x);
    }

    public int pop() {
        while(!mainStack.empty()){
            subStack.add(mainStack.pop());
        }

        int result = subStack.pop();

        mainStack = new Stack<>();
        while(!subStack.empty()){
            mainStack.add(subStack.pop());
        }

        subStack = new Stack<>();
        return result;
    }

    public int peek() {
        while(!mainStack.empty()){
            subStack.add(mainStack.pop());
        }

        int result = subStack.peek();

        mainStack = new Stack<>();
        while(!subStack.empty()){
            mainStack.add(subStack.pop());
        }

        subStack = new Stack<>();
        return result;
    }

    public boolean empty() {
        return mainStack.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();
 * boolean param_4 = obj.empty();
 */