LeetCode 剑指 Offer 09. 用两个栈实现队列(swift)

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]

class CQueue {
    var inputList:[Int] = []
    var outputList:[Int] = []
    
    init() {
        
    }
    
    func appendTail(_ value: Int) {
        inputList.append(value)
    }
    
    func deleteHead() -> Int {
        // 把inputList的放到outputList然后退栈
        if outputList.isEmpty == true {
            while inputList.isEmpty == false {
                outputList.append(inputList.popLast()!)
            }
            if outputList.isEmpty == false {
                return outputList.popLast()!
            }
            else {
                return -1
            }
        }
        else {
            return outputList.popLast()!
        }
    }
}

/**
 * Your CQueue object will be instantiated and called as such:
 * let obj = CQueue()
 * obj.appendTail(value)
 * let ret_2: Int = obj.deleteHead()
 */

let obj = CQueue()
obj.appendTail(5)
obj.appendTail(4)
let ret_2: Int = obj.deleteHead()
obj.appendTail(3)
let ret_3: Int = obj.deleteHead()