第一天 09. 用两个栈实现队列

题目

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","deleteHead"]
[[],[4],[],[],[]]
输出：[null,null,4,-1,-1]

示例2

输入：
["CQueue","deleteHead","appendTail","appendTail","deleteHead","deleteHead"]
[[],[],[3],[8],[],[]]
输出：[null,-1,null,null,3,8]

Swift

//用两个栈实现队列
//自定义栈结构
class AStack {
    var list = [Int]()
    func pop()-> Int{
        if list.isEmpty == true {
            //异常处理，返回-1
            return -1
        }
        return list.removeLast()
    }
    func push(obj:Int) {
        list.append(obj)
    }
    func isEmpty() -> Bool {
        return list.isEmpty
    }
}

class CQueue {
    var inStack:AStack
    var outStack:AStack
    init() {
        inStack = AStack()
        outStack = AStack()
    }
    
    func appendTail(_ value: Int) {
        inStack.push(obj: value)
    }
    
    func deleteHead() -> Int {
        if outStack.isEmpty() == true {
             while inStack.isEmpty() == false {
                 outStack.push(obj:inStack.pop())
             }
        }
        return outStack.pop()
    }
}

var que = CQueue()
que.appendTail(1)
que.deleteHead()
que.deleteHead()
que.deleteHead()

Java

待更新

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