【数据结构】堆

• 前言
• 1 代码
• 总结

C#居然没有堆的数据结构，那就只能自己实现了。

实现参考：《挑战程序设计竞赛》

mCompareFunc判断a小于b时为小跟堆，否则为大根堆。

public class Heap
{
     List mHeapList = new List();
     Func mCompareFunc;

     public int Size => mHeapList.Count;

     public Heap(Func compareFunc)
     {
         mCompareFunc = compareFunc;
     }

     public void Push(T value)
     {
         int index = mHeapList.Count;
         mHeapList.Add(value);
         while (index > 0)
         {
             int parent = (index - 1) / 2;
             if (mCompareFunc(mHeapList[parent], value)) break;

             mHeapList[index] = mHeapList[parent];
             index = parent;
         }
         mHeapList[index] = value;
     }

     public T Pop()
     {
         if (Empty())
         {
             throw new ArgumentOutOfRangeException("堆为空！");
         }

         T ret = mHeapList[0];
         int size = mHeapList.Count - 1;
         T x = mHeapList[size];
         int index = 0;
         while(index * 2 + 1 < size)
         {
             int leftChildIndex = index * 2 + 1;
             int rightChildIndex = index * 2 + 2;
             if (leftChildIndex < size && mCompareFunc(mHeapList[rightChildIndex], mHeapList[leftChildIndex])) 
                 leftChildIndex = rightChildIndex;
             
             // 已经没有大小颠倒则退出
             if (!mCompareFunc(mHeapList[leftChildIndex], x)) break;

             mHeapList[index] = mHeapList[leftChildIndex];
             index = leftChildIndex;
         }
         mHeapList[index] = x;
         mHeapList.RemoveAt(mHeapList.Count - 1);
         return ret;
     }

     public T Top()
     {
         return mHeapList[0];
     }

     public bool Empty()
     {
         return mHeapList.Count == 0;
     }
 }

如果要使用优先队列，那么其中一种实现就是把堆封装一下就可以了。