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 /article/4676280.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<T>
{
IComparer<T> comparer;
T[] heap;

public int Count { get; private set; }

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

public PriorityQueue(int capacity, IComparer<T> comparer)
{
this.comparer = (comparer == null) ? Comparer<T>.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
;
for (var n2 = n / 2; n > 0 && comparer.Compare(v, heap[n2]) > 0; n = n2, n2 /= 2) heap
= heap[n2];
heap
= v;
}

void SiftDown(int n)
{
var v = heap
;
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
= heap[n2];
}
heap
= 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 : IComparer<KeyValuePair<double, 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)
{
PriorityQueue<KeyValuePair<double, int>>  que = new PriorityQueue<KeyValuePair<double, 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
*/