力扣简232 用栈实现队列

其实同225题的感觉 一个是用栈实现队列 一个是用队列实现栈

栈队列等的定义，一不用就忘，我无语！而且栈用push和pop，用别的会搞乱！

class MyQueue {
    
    Deque<Integer> stack1;
    Deque<Integer> stack2;

    public MyQueue() {
        stack1=new LinkedList<Integer>();
        stack2=new LinkedList<Integer>();
    }
    
    public void push(int x) {
        while(!stack1.isEmpty()) {
            stack2.push(stack1.poll());
        }
        stack1.push(x);
        while(!stack2.isEmpty()) {
            stack1.push(stack2.poll());
        }
    }
    
    public int pop() {
        return(stack1.pop());
    }
    
    public int peek() {
        return(stack1.peek());
    }
    
    public boolean empty() {
        return stack1.isEmpty();
    }
}

 

//看了一眼题解2：通过出栈来分摊入栈的时间复杂度。 明天再写吧

//还有用front来标记队列头的元素 取队列头元素简单  2022 0603补充

class MyQueue {
    
    Deque<Integer> stack1;
    Deque<Integer> stack2;
    int flag;

    public MyQueue() {

        stack1=new LinkedList<Integer>();
        stack2=new LinkedList<Integer>();
    }
    
    public void push(int x) {
        if(stack1.isEmpty()) {
//            stack1.push(x);
            flag=x;
        }
        stack1.push(x);
    }
    
    public int pop() {
        if(!stack2.isEmpty())
            return stack2.pop();
        while(!stack1.isEmpty()) {
            stack2.push(stack1.pop());
        }
        return stack2.pop();
    }
    
    public int peek() {
        if(!stack2.isEmpty()) {
            return stack2.peek();
        }
        return flag;
    }
    
    public boolean empty() {
        return stack1.isEmpty()&&stack2.isEmpty();
    }
}