Unity C# 优先队列

实现了支持泛型的优先队列，解决Unity官方不提供优先队列的问题。

API

属性和字段	解释
size	队列的长度
capacity	队列的容量
IsEmpty	返回队列是否为空
Top	返回队列第一个元素

枚举	解释
PriorityQueueMode.less	最小优先队列
PriorityQueueMode.equal	只会将相等的排在一起
PriorityQueueMode.greator	最大优先队列

函数	功能
Push	入队一个元素
Pop	出队一个元素
Peek	返回第一个元素
Clear	清空队列

示例

PriorityQueue<int> priorityQueue = new PriorityQueue<int>((a, b) => {
            if (a < b) return -1;
            else if (a == b) return 0;
            else if (a > b) return 1;
            return 0;
});

priorityQueue.Push(8);
priorityQueue.Push(9);
priorityQueue.Push(3);
priorityQueue.Push(2);
priorityQueue.Push(7);
priorityQueue.Push(5);
priorityQueue.Push(0);

while (!priorityQueue.IsEmpty) {
    Debug.Log(priorityQueue.Top);
    priorityQueue.Pop();
}

实现

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using System;

namespace YBZ.Algorithm {
    public class PriorityQueue<T> where T : new ()
    {
        public int size;
        public int capacity;
        private T[] elements;

        // 是否为空
        public bool IsEmpty { get => size == 0; }

        /// 返回顶部元素
        public T Top { get => elements[0]; }

        /// 优先队列的模式
        private PriorityQueueMode _comparator;

        public enum PriorityQueueMode {
            less = -1, // 最小优先队列
            equal = 0, // 相等的排在一起
            greater = 1 // 最大优先队列
        }

        /// <summary>
        /// 以CMP(a,b) 为例：
        /// 当a>b时，返回1，表示放右边
        /// 当a==b时，返回0，表示不变
        ///  当a<b时，返回-1，表示放左边
        /// </summary>
        private Func<T,T,int> CMP;
        
        /// <summary>
        /// 构造函数, 必须实现
        /// </summary>
        /// <param name="CMP"></param>
        /// <param name="capacity"></param>
        /// <param name="priorityQueueMode"></param>
        public PriorityQueue(Func<T,T,int> CMP, PriorityQueueMode priorityQueueMode = PriorityQueueMode.less, int capacity = 1) {
            this.CMP = CMP;
            this.size = 0; // 数组索引从0开始
            this.capacity = capacity;
            this.elements = new T[capacity];
            this._comparator = priorityQueueMode;
        }

        /// <summary>
        /// 入队
        /// </summary>
        /// <param name="value"></param>
        public void Push(T value) {
            if (size == capacity) {
                ExpandCapacity();
            }
            elements[size++] = value;

            ShiftUp();
        }

        /// <summary>
        /// 出队
        /// </summary>
        public void Pop() {
            if(size == 0) {
                return;
            }
            size--;
            Swap(ref elements[0], ref elements[size]);

            ShiftDown();
        }

        /// <summary>
        /// 清空队列
        /// </summary>
        public void Clear() {
            size = 0;
        }

        /// <summary>
        /// 返回位于Queue开始处的对象但不将其移除。
        /// </summary>
        /// <returns>返回第一个队列中元素</returns>
        public T Peek() {
            return Top;
        }

        /// <summary>
        /// 扩展队列的容量
        /// </summary>
        private void ExpandCapacity() {
            capacity = Mathf.CeilToInt(capacity * 1.5f);
            T[] temp = new T[capacity];

            for (int i = 0; i < elements.Length; i++) {
                temp[i] = elements[i];
            }
            elements = temp;
        }
        
        // 从下到上 重排序 
        private void ShiftUp() {
            int cur = size - 1 ;
            int parent = ( cur -1 ) >> 2;
            while (cur > 0) 
            {
                if (CMP(elements[cur],elements[parent]) == (int)_comparator) {
                    Swap(ref elements[cur], ref elements[parent]);
                    cur = parent;
                    parent = (cur - 1) >> 2;
                } else break;
            }
        }

        // 从上到下 重排序
        private void ShiftDown() {
            int cur = 0;
            int child = 1;
            while (child < size) {
                if (child + 1 < size && CMP(elements[child +1], elements[child]) == (int)_comparator) {
                    child++;
                }

                if (CMP(elements[child], elements[cur]) == (int)_comparator){

                    Swap(ref elements[child], ref elements[cur]);
                    cur = child;
                    child = cur << 1 + 1;
                } else break;
            }
        }

        /// <summary>
        /// 交换传入的两个元素
        /// </summary>
        /// <param name="lhs"></param>
        /// <param name="rhs"></param>
        private void Swap(ref T lhs,ref T rhs) {
            T temp = lhs;
            lhs = rhs;
            rhs = temp;
        }

        /// <summary>
        /// 返回队列中的所有元素,对于ToString()函数，值类型会返回值，引用类型会返回数据类型
        /// </summary>
        /// <returns></returns>
        public override string ToString() {
            string result = "";
            foreach (var v in elements) {
                result += v.ToString();
            }
            return result;
        }
    }
}