剑指Offer系列_09_用两个栈实现队列

package leetcode.sword_to_offfer.day01;

import java.util.LinkedList;

/**
 * 用两个栈实现一个队列。队列的声明如下，请实现它的两个函数 appendTail 和 deleteHead ，
 * 分别完成在队列尾部插入整数和在队列头部删除整数的功能。(若队列中没有元素，deleteHead操作返回 -1 )
 * <p>
 * 示例 1：
 * <p>
 * 输入：
 * ["CQueue","appendTail","deleteHead","deleteHead"]
 * [[],[3],[],[]]
 * 输出：[null,null,3,-1]
 * 示例 2：
 * <p>
 * 输入：
 * ["CQueue","deleteHead","appendTail","appendTail","deleteHead","deleteHead"]
 * [[],[],[5],[2],[],[]]
 * 输出：[null,-1,null,null,5,2]
 * <p>
 * <p>
 * Your CQueue object will be instantiated and called as such:
 * CQueue obj = new CQueue();
 * obj.appendTail(value);
 * int param_2 = obj.deleteHead();
 *
 * @author soberw
 * @Classname CQueue
 * @Description
 * @Date 2022-02-07 8:34
 */
public class CQueue {
    private final LinkedList<Integer> list;
    private final LinkedList<Integer> listOut;

    public CQueue() {
        list = new LinkedList<>();
        listOut = new LinkedList<>();
        listOut.add(null);
    }

    public void appendTail(int value) {
        list.add(value);
        listOut.add(null);
    }

    public int deleteHead() {
        if (list.isEmpty()) {
            listOut.add(-1);
            listOut.pop();
            return -1;
        }
        Integer removeFirst = list.removeFirst();
        listOut.add(removeFirst);
        return removeFirst;
    }
}