C#实现优先队列 基于二叉堆 附使用案例

前言

• 想用下C#的优先队列，结果发现居然没有，简直蛋疼。。。
• 感谢 http://www.cnblogs.com/skyivben/archive/2009/04/18/1438731.html 博主的实现
• 我借用博主的优先队列实现，写了测试程序，感觉还可以，这里放出来当个使用案例吧~

转载实现

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DynamicTrafficAssignment.Core
{
    public class PriorityQueue
    {
        IComparer comparer;
        T[] heap;

        public int Count { get; private set; }

        public PriorityQueue() : this(null) { }
        public PriorityQueue(int capacity) : this(capacity, null) { }
        public PriorityQueue(IComparer comparer) : this(16, comparer) { }

        public PriorityQueue(int capacity, IComparer comparer)
        {
            this.comparer = (comparer == null) ? Comparer.Default : comparer;
            this.heap = new T[capacity];
        }

        public void Push(T v)
        {
            if (Count >= heap.Length) Array.Resize(ref heap, Count * 2);
            heap[Count] = v;
            SiftUp(Count++);
        }

        public T Pop()
        {
            var v = Top();
            heap[0] = heap[--Count];
            if (Count > 0) SiftDown(0);
                return v;
        }

        public T Top()
        {
            if (Count > 0) return heap[0];
            throw new InvalidOperationException("优先队列为空");
        }

        void SiftUp(int n)
        {
            var v = heap[n];
            for (var n2 = n / 2; n > 0 && comparer.Compare(v, heap[n2]) > 0; n = n2, n2 /= 2) heap[n] = heap[n2];
                heap[n] = v;
        }

        void SiftDown(int n)
        {
            var v = heap[n];
            for (var n2 = n * 2; n2 < Count; n = n2, n2 *= 2)
            {
                if (n2 + 1 < Count && comparer.Compare(heap[n2 + 1], heap[n2]) > 0) n2++;
                if (comparer.Compare(v, heap[n2]) >= 0) break;
                heap[n] = heap[n2];
            }
            heap[n] = v;
        }
    }



}

使用案例

说明

• 我用了个键值对，作为在优先队列中的元素类型
• 手写了比较类，实现的是一个小值优先的队列
• 和eps比，是为了防止double的精度问题，具体使用可以改变设置

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using DynamicTrafficAssignment.Core;
namespace DTATest
{
    class Program
    {
        const double eps = 1e-8;
        public class PairCompare : IComparerdouble, int>>
        {
            public int Compare(KeyValuePair<double, int> x, KeyValuePair<double, int> y)
            {
                if (Math.Abs(y.Key - x.Key) < eps)
                {
                    return 0;
                }
                if (x.Key > y.Key)
                    return -1;
                else
                    return 1;
            }
        }
        static void Main(string[] args)
        {
            PriorityQueuedouble, int>>  que = new PriorityQueuedouble, int>>(new PairCompare());
            for (int i = 0; i < 5; i++)
            {
                var str = Console.ReadLine().Split(' ');
                que.Push( new KeyValuePair<double, int>(Double.Parse(str[0]), Int32.Parse(str[1]) ) );
            }
            while (que.Count > 0)
            {
                var tmp = que.Pop();
                Console.WriteLine(tmp.Key + "," + tmp.Value);
            }
            Console.Read();
        }
    }

}
///输入
/*
0.1 2
0.1 1
-1.9 200
0 9
10000.42 3
*/
///输出
/*
-1.9,200
0,9
0.1,2
0.1,1
10000.42,3
*/