普通隊(duì)列

public class Queue<T> {
    public var list: [T]
    private var front: Int
    private var rear: Int
    private var size: Int

    public init(_ count: Int) {
        size = count+1
        list = [T](repeating: 0 as! T, count: count)
        front = 0
        rear = 0
    }

    public func enQueue(item: T) {
        if full() {
            return
        }
        list[rear] = item
        rear += 1
    }
    
    public func deQueue() -> T? {
        if empty() {
            return nil
        }
        let temp = list[front]
        front += 1
        return temp
    }
    
    public func empty() -> Bool {
        return front == rear
    }
    
    public func full() -> Bool {
        return rear == size-1
    }
    
    public func count() -> Int {
        return rear - front
    }
}

循環(huán)隊(duì)列

普通隊(duì)列會造成假溢出的問題亭姥，使用循環(huán)隊(duì)列解決該問題，具體問題分析看這里
leetcode 641. 設(shè)計(jì)循環(huán)雙端隊(duì)列

class CircularDeque {

    public var capacity: Int
    private var deque: [Int]
    private var front: Int
    private var rear: Int
    
    init(_ k: Int) {
        capacity = k + 1 //犧牲一個(gè)空間，方便判斷是否滿隊(duì)列 (rear + 1) % capacity = front
        deque = [Int](repeating: 0, count: capacity)
        front = 0
        rear = 0
    }
    
    func insertFront(_ value: Int) -> Bool {
        if isFull() {return false}
        front = (front - 1 + capacity) % capacity
        deque[front] = value
        return true
    }
    
    func insertLast(_ value: Int) -> Bool {
        if isFull() {return false}
        rear = (rear + 1) % capacity
        deque[rear] = value
        return true
    }
    
    func deleteFront() -> Bool {
        if isEmpty() {return false}
        front = (front + 1) % capacity
        return true
    }
    
    func deleteLast() -> Bool {
        if isEmpty() {return false}
        rear = (rear - 1 + capacity) % capacity
        return true
    }
    
    func getFront() -> Int {
        if isEmpty() {return -1}
        return deque[front]
    }
    
    func getRear() -> Int {
        if isEmpty() {return -1}
        return deque[(rear - 1 + capacity) % capacity] //取尾部時(shí)，需要向后移動一下取帮哈，因?yàn)閞ear指針總是指向最后一個(gè)值的下一個(gè)指針
    }
    
    func isEmpty() -> Bool {
        return front == rear
    }
    
    func isFull() -> Bool {
        return (rear + 1) % capacity == front
    }
}