来自菜鸟的日程-------c语言基础篇19（排序3----归并，快排优化）

#include<stdio.h>
#include<math.h>
#include<stdlib.h>
#include<assert.h>
#include <time.h>
//归并排序

void Merge(int *arr,int len,int gap)
{
	int *brr = (int *)malloc(sizeof(int)*len);
	assert(brr != NULL);
	int i = 0;//brr下标
	int start1 = 0;
	int end1 = start1 + gap-1;
	int start2 = end1 + 1;
	int end2 = start2 + gap - 1 < len - 1 ? start2 + gap -1 : len - 1;
	//当有两个归并段时
	while(start2 < len)
	{
		//当两个归并段还没有比较完的时候
		while(start1 <= end1 &&  start2 <= end2)
		{
			if(arr[start1] <= arr[start2])
			{
				brr[i++] = arr[start1++];
				 
			}
			else
			{
				brr[i++] = arr[start2++];
			}
		}
		while(start1 <= end1)
		{
			brr[i++] = arr[start1++];
		}
		while(start2 <= end2)
		{
			brr[i++] = arr[start2++];
		}
		// 找两个新的归并段
		start1 = end2 +1;
		end1 = start1 + gap-1;
		start2 = end1 + 1;
		end2 = start2 + gap - 1 < len - 1 ? start2 + gap -1:len - 1;
	}
	while(start1 < len)
	{
		brr[i++] = arr[start1++];
	}

	for(int i = 0;i < len;i++)
	{
		arr[i] = brr[i];
	}

}
		 
void MergeSort(int *arr,int len)
{
	for(int i = 1;i < len;i *= 2)
	{
		 Merge(arr,len,i);
	}
}
void Show(int *arr,int len)
{
	for(int i = 0;i < len;i++)
	{
		printf("%d ",arr[i]);
	}
	printf("\n");
}

//快排的优化

int Partion(int *arr,int low,int high)
{
	int tmp = arr[low];
	while(low < high)
	{
		while(low < high && arr[high] >= tmp)
		{
			high--;
		}
		if(low >= high)
		{
			break;
		}
		else
		{
			arr[low] = arr[high];
		}
		while(low < high && arr[low] <= tmp)
		{
			low++;
		}
		if(low >= high)
		{
			break;
		}
		else
		{
			arr[high] = arr[low];
		}
	}
	arr[low] = tmp;
	return low;
}
void Swap(int *arr,int start,int end)
{
	int tmp = arr[start];
	arr[start] = arr[end];
	arr[end] = tmp;
}

//优化方式一：当待排序的区间中，待排序的个数小于某一个数量级的时候,使用插入排序
// (插入排序越有序越快)
// 时间复杂度:O（n）

void InsertSort(int *arr,int low,int high)
{
	for(int i = low+1;i <= high;i++)
	{
		int tmp = arr[i];
		int j = 0;
		for(j = i-1;j >= low;j--)
		{
			if(arr[j] > tmp)
			{
				arr[j+1] = arr[j];
			}
			else
			{
				break;
			}
		}
		arr[j+1] = tmp;
	}
}
void Quick1(int *arr,int start,int end)
{
	//InsertSort(arr,start,end);
	if((end-start)+1 <= 10000)
	{
		InsertSort(arr,start,end);
	}
} 
void QuickSort1(int *arr,int len)
{
	Quick1(arr,0,len-1);
}

//排序方式2：随机选取基准法

void Quick2(int *arr,int start,int end)
{
	srand((unsigned int)time(NULL));
	Swap(arr, start,rand() % (end-start)+start);
	int par = Partion(arr,start,end);//O(n)
	//左边   
	if(par > start + 1)
	{
		Quick2(arr,start,par - 1);//log(2n)
	}
	//右边
	if(par < end - 1)
	{
        Quick2(arr,par + 1,end);
	}
} 
void QuickSort2(int *arr,int len)
{
	Quick2(arr,0,len-1);
}

//聚集相同元素基准法

void FocusNumPar(int *arr,int low,int par,int high,int *left,int *right)
{
	if(low < high)
	{
		int parLeft = par-1;
		for(int i = par - 1;i >= low;i--)
		{
			if(arr[i] == arr[par])
			{
				if(i != parLeft)
				{
					Swap(arr,i,parLeft);
					parLeft--;
				}
				else
				{
					parLeft--;
				}
			}
		}
		*left = parLeft;
		int parRight = par+1;
		for(int i = par+1;i <= high;i++)
		{
			if(arr[i] == arr[par])
			{
				if(i != parRight)
				{
					Swap(arr,i,parRight);
					parRight++;
				}
				else
				{
					parRight++;
				}
			}
		}
		*right = parRight;
	}
}
void Quick3(int *arr,int start,int end)
{ 
	int par = Partion(arr,start,end);//O(n)
	int left = 0;
	int right = 0;
	FocusNumPar(arr,start,par,end,&left,&right);
	//左边 
	if(left >= start+1)//说明左边有两个数据以上
	{
		Quick3(arr,start,left);
	}
	//右边
	if(right <= end-1)
	{
		Quick3(arr,right,end);
	}
}
void QuickSort3(int *arr,int len)
{
	Quick3(arr,0,len-1);
}

//1 2 3 4 5 6
//排序方式3：三分取中法

void SelectPivotMedianOfThree(int *arr,int low,int high) 
{
	int mid = (high-low)/2 + low;//(high+low)>>1;
	//arr[mid]<=arr[low]<=arr[high];
	if(arr[mid] > arr[low])
	{
		Swap(arr,mid,low);
	}//arr[mid] <= arr[low]
	if(arr[low] > arr[high]) 
	{
		Swap(arr,low,high);
	}//arr[low] <= arr[high]
	if(arr[mid] > arr[high])
	{
		Swap(arr,mid,high);
	}//arr[mid] <= arr[high]
	 
}
void Quick4(int *arr,int start,int end)
{ 
	int par = Partion(arr,start,end);
	SelectPivotMedianOfThree(arr,start,end); 
	if(par >= start+1)//说明左边有两个数据以上
	{
		Quick4(arr,start,par-1); 
	}
	if(par <= end-1)
	{
		Quick4(arr,par+1,end); 
	}
} 
void QuickSort4(int *arr,int len)
{
	Quick4(arr,0,len-1);
}


int main()
{
	int arr[10000] = {};
	int len = sizeof(arr)/sizeof(arr[0]);
	srand(time(NULL));
	for(int i = 0;i < len;i++)
	{
		arr[i] = rand()%10000;
	}
	//MergeSort(arr,len);
	//QuickSort1(arr,len);
	//QuickSort2(arr,len);
	//QuickSort3(arr,len);
	//QuickSort4(arr,len);
	Show(arr,len);
	return 0;
}