LeetCode 剑指offer 09.用两个栈实现队列

题目描述

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 )

这道题很简单，主要理解栈与队列的区别，注意细节就可以

题解

c++

cpp 复制代码

class CQueue {
public:
    stack<int> s1, s2;
    CQueue() {
        while (!s1.empty()) {
            s1.pop();
        }
        while (!s2.empty()) {
            s2.pop();
        }
    }
    
    void appendTail(int value) {
        s1.push(value);
    }
    
    int deleteHead() {
        if (s2.empty()) {
            while(!s1.empty()) {
                s2.push(s1.top());
                s1.pop();
            }
        }
        if (s2.empty()) {
            return -1;
        } else {
            int app = s2.top();
            s2.pop();
            return app;
        }
    }
};

/**
 * Your CQueue object will be instantiated and called as such:
 * CQueue* obj = new CQueue();
 * obj->appendTail(value);
 * int param_2 = obj->deleteHead();
 */

cpp 复制代码

type CQueue struct {
    inStack, outStack []int
}

func Constructor() CQueue {
    return CQueue{}
}

func (this *CQueue) AppendTail(value int)  {
    this.inStack = append(this.inStack, value)
}

func (this *CQueue) DeleteHead() int {
    if len(this.outStack) == 0 {
        if len(this.inStack) == 0 {
            return -1
        }
        this.in2out()
    }
    value := this.outStack[len(this.outStack)-1]
    this.outStack = this.outStack[:len(this.outStack)-1]
    return value
}

func (this *CQueue) in2out() {
    for len(this.inStack) > 0 {
        this.outStack = append(this.outStack, this.inStack[len(this.inStack)-1])
        this.inStack = this.inStack[:len(this.inStack)-1]
    }
}