力扣232—用栈实现队列(思路+代码)

链接
栈实现队列

思路：创建两个栈，入队：元素先入a。出队：b中为空且a不为空时，让a中元素入b(保证了后入的元素后出)

1.创建两个栈

 	Stack<Integer> a;
    Stack<Integer> b;
    public MyQueue() {
        a = new Stack<>();
        b = new Stack<>();
    }

2.入队

public void push(int x) {
        a.push(x);
    }

3.出队

 public int pop() {
        if(b.isEmpty()){//b中全部出完了 才能把a入b，保证后入后出，先入先出
         while(!a.isEmpty()){
            b.push(a.pop());
            }
        }
        return b.pop();
    }

4.查看栈顶

 public int peek() {
         if(b.isEmpty()){
         while(!a.isEmpty()){
            b.push(a.pop());
            }
        }
        return b.peek();
    }

完整代码

class MyQueue {
    Stack<Integer> a;
    Stack<Integer> b;
    public MyQueue() {
        a = new Stack<>();
        b = new Stack<>();
    }
    
    public void push(int x) {
        a.push(x);
    }
    
    public int pop() {
        if(b.isEmpty()){//b中全部出完了 才能把a入b，保证后入后出，先入先出
         while(!a.isEmpty()){
            b.push(a.pop());
            }
        }
        return b.pop();
    }
    
    public int peek() {
         if(b.isEmpty()){
         while(!a.isEmpty()){
            b.push(a.pop());
            }
        }
        return b.peek();
    }
    
    public boolean empty() {
        return (a.isEmpty() && b.isEmpty());
    }
}

如果对你有所帮助，一键三连！

运行结果