5. 用两个栈实现队列

双栈实现队列

原创于 2019-12-23 06:58:52 发布 · 139 阅读

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文章目录

1. 正常两个栈
2. 栈+递归栈

1. 正常两个栈

/**
 * @Classname Solution
 * @Description 两个栈实现队列
 * @Date 2019/12/17 16:01
 * @Created by Cheng
 */
public class Solution {
    Stack<Integer> stack1 = new Stack<Integer>();
    Stack<Integer> stack2 = new Stack<Integer>();

    public void push(int node) {
        stack1.push(node);
    }

    public int pop() {
        if (stack2.isEmpty()) {
            while (!stack1.isEmpty()) {
                stack2.push(stack1.pop());
            }
        }
        // 如果此时stack2依旧为空，则整个数据为空
        return stack2.pop();
    }
}

2. 栈+递归栈

/**
 * @Classname Solution
 * @Description 两个栈实现队列
 * @Date 2019/12/17 16:01
 * @Created by Cheng
 */
public class Solution {
    Stack<Integer> stack = new Stack<Integer>();

    public void push(int node) {
        stack.push(node);
    }
    
    public int pop() {
        if (stack.size() == 1) {
            return stack.pop();
        }
        int temp = stack.pop();
        int ret = pop();
        // 记得放回去
        stack.push(temp);
        return ret;
    }
}