LeetCode高频面试60天打卡日记Day01

Day01

Idea:
1、维护两个队列 q1接收输入数据 q2作为输出队列
2、push操作，q1接收新来的数据，再将q2中存放的元素全部加入q1，此时q1 = new data + q2 data
3、将q1 和 q2的引用交换，始终保证q1为空接收新来数据

class MyStack {
    
    
    private Queue<Integer> q1; //输入
    private Queue<Integer> q2; //输出
    private int top;
    /** Initialize your data structure here. */
    public MyStack() {
    
    
        q1 = new LinkedList<Integer>();
        q2 = new LinkedList<Integer>();
    }
    
    /** Push element x onto stack. */
    public void push(int x) {
    
    
        q1.offer(x); //q1接收数据，将q2中所有数据复制到q1，保证先来的数据在后面，新来的数据在前面
        while(!q2.isEmpty()){
    
    
            q1.offer(q2.poll());
        }
        Queue temp = q1;
        q1 = q2;
        q2 = temp;
    }
    
    /** Removes the element on top of the stack and returns that element. */
    public int pop() {
    
    
        return q2.poll();
    }
    
    /** Get the top element. */
    public int top() {
    
    
        return q2.peek();
    }
    
    /** Returns whether the stack is empty. */
    public boolean empty() {
    
    
        return q2.isEmpty();
    }
}

/**
 * Your MyStack object will be instantiated and called as such:
 * MyStack obj = new MyStack();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 = obj.top();
 * boolean param_4 = obj.empty();
 */