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剑指 Offer 09. 用两个栈实现队列---java

作者:互联网

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 )

示例 1:

输入:
["CQueue","appendTail","deleteHead","deleteHead"]
[[],[3],[],[]]
输出:[null,null,3,-1]
示例 2:

输入:
["CQueue","deleteHead","appendTail","appendTail","deleteHead","deleteHead"]
[[],[],[5],[2],[],[]]
输出:[null,-1,null,null,5,2]
提示:

1 <= values <= 10000
最多会对 appendTail、deleteHead 进行 10000 次调用

class CQueue {
    Stack<Integer> stack1;
    Stack<Integer> stack2;
    public CQueue() {
        stack1 = new Stack<>();
        stack2 = new Stack<>();
    }
    
    public void appendTail(int value) {
        stack1.push(value);     //入stack1栈
    }
    //两个栈模拟队列
    public int deleteHead() {
        if(!stack2.isEmpty())return stack2.pop();   //stack1栈有元素,则返回
        if(stack1.isEmpty())return -1;              //判断stack1栈是都有元素,没有返回-1
        while(!stack1.isEmpty()){                   //stack1栈有元素,需要移到stack2栈中,这样技能先进先出
            
            stack2.push(stack1.pop());
        }
        return stack2.pop();
    }
}

标签:deleteHead,appendTail,Offer,队列,09,---,null,stack2,stack1
来源: https://www.cnblogs.com/xiaochaofang/p/16030656.html