归并排序算法思想：
归并排序（MERGE-SORT）是建立在归并操作上的⼀种有效的排序算法,该算法是采用分治法（Divide and Conquer）的⼀个非常典型的应用。将已有序的子序列合并，得到完全有序的序列；即先使每个子序列有序，再使子序列段间有序。若将两个有序表合并成⼀个有序表，称为二路归并。
分治的思想：将待排序的数组不断分割成更小的子数组，直到每个子数组只包含一个元素。
具体过程：
找到数组的中间位置，一般是通过 mid = left + (right - left) / 2 来计算（为了防止越界），left 和 right 分别表示当前数组范围的起始和结束索引。
然后递归地对数组的左半部分（索引范围从 left 到 mid）和右半部分（索引范围从 mid + 1 到 right）进行同样的分割操作，直到子数组的长度为 1。
代码实现：
cpp复制代码
void _MergeSort(int* arr, int left, int right,int*tmp)
{
//分解
if (left >= right)
{
return;
}
//根据mid将[left,right]划分为左右两个序列[left,mid] [mid+1,right]
int mid = left + (right - left) / 2;
_MergeSort(arr, left, mid,tmp);
_MergeSort(arr, mid+1, right,tmp);
//合并[left,mid] [mid+1,right]
int begin1 = left, end1 = mid;
int begin2 = mid+1, end2 = right;
int index = left;
while (begin1 <= end1 && begin2 <= end2)
{
if (arr[begin1] < arr[begin2])
{
tmp[index++] = arr[begin1++];
}
else
{
tmp[index++] = arr[begin2++];
}
}
//要么begin1越界
//要么begin2越界
while (begin1 <= end1)
{
tmp[index++] = arr[begin1++];
}
while (begin2 <= end2)
{
tmp[index++] = arr[begin2++];
}
for (int i = left; i <= right; i++)
{
arr[i] = tmp[i];
}
}
//归并排序
void MergeSort(int* arr, int n)
{
int* tmp = (int*)malloc(sizeof(int)*n);
//[0,n-1]
_MergeSort(arr, 0, n - 1,tmp);
free(tmp);
tmp = NULL;
}
提醒：
test.c:
cpp复制代码
#include"Sort.h"
void printArr(int* arr, int n)
{
for (int i = 0; i < n; i++)
{
printf("%d ", arr[i]);
}
printf("\n");
}
void test01()
{
int a[] = { 5,3,9,6,2,4,7,1,8 };
//int a[] = { 6,1,2,7,9,3 };
int n = sizeof(a) / sizeof(a[0]);
printf("排序之前：");
printArr(a, n);
//InsertSort(a, n);
//ShellSort(a, n);
//SelectSort(a, n);
//HeapSort(a, n);
//BubbleSort(a, n);
//QuickSort(a, 0, n - 1);
//QuickSortNorR(a, 0, n - 1);
MergeSort(a, n);
//CountSort(a, n);
//MergeSortNonR(a, n);
printf("排序之后：");
printArr(a, n);
}
void TestOP()
{
srand(time(0));
const int N = 100000;
int* a1 = (int*)malloc(sizeof(int) * N);
int* a2 = (int*)malloc(sizeof(int) * N);
int* a3 = (int*)malloc(sizeof(int) * N);
int* a4 = (int*)malloc(sizeof(int) * N);
int* a5 = (int*)malloc(sizeof(int) * N);
int* a6 = (int*)malloc(sizeof(int) * N);
int* a7 = (int*)malloc(sizeof(int) * N);
for (int i = 0; i < N; ++i)
{
a1[i] = rand();
a2[i] = a1[i];
a3[i] = a1[i];
a4[i] = a1[i];
a5[i] = a1[i];
a6[i] = a1[i];
a7[i] = a1[i];
}
int begin1 = clock();
InsertSort(a1, N);
int end1 = clock();
int begin2 = clock();
ShellSort(a2, N);
int end2 = clock();
int begin3 = clock();
SelectSort(a3, N);
int end3 = clock();
int begin4 = clock();
HeapSort(a4, N);
int end4 = clock();
int begin5 = clock();
QuickSort(a5, 0, N - 1);
int end5 = clock();
//int begin6 = clock();
//MergeSort(a6, N);
//int end6 = clock();
int begin7 = clock();
BubbleSort(a7, N);
int end7 = clock();
printf("InsertSort:%d\n", end1 - begin1);
printf("ShellSort:%d\n", end2 - begin2);
printf("SelectSort:%d\n", end3 - begin3);
printf("HeapSort:%d\n", end4 - begin4);
printf("QuickSort:%d\n", end5 - begin5);
//printf("MergeSort:%d\n", end6 - begin6);
printf("BubbleSort:%d\n", end7 - begin7);
free(a1);
free(a2);
free(a3);
free(a4);
free(a5);
free(a6);
free(a7);
}
int main()
{
test01();
//TestOP();
return 0;
}
