225. 用队列实现栈

题目链接：https://leetcode-cn.com/problems/implement-stack-using-queues/

执行用时：0 ms, 在所有 Swift 提交中击败了100.00%的用户
内存消耗：14 MB, 在所有 Swift 提交中击败了42.62%的用户

class MyStack {
    var inQueue = [Int]()
    var outQueue = [Int]()
    init() {
        inQueue = []
        outQueue = []
    }

    func push(_ x: Int) {
        inQueue.append(x)
    }
    func swap() {
        var temp = inQueue
        inQueue = outQueue
        outQueue = temp
    }
    func pop() -> Int {
        while inQueue.count > 1 {
            outQueue.append(inQueue.removeFirst())
        }
        var front = inQueue.removeFirst()
        swap()
        return front
    }

    func top() -> Int {
        while inQueue.count > 1 {
            outQueue.append(inQueue.removeFirst())
        }
        var front = inQueue.first
        outQueue.append(inQueue.removeFirst())
        swap()
        return front!
    }

    func empty() -> Bool {
        return inQueue.isEmpty && outQueue.isEmpty
    }
}