//归并排序
将原始数组A[0:n-1]中的元素分成两个大小大致相同的子数组:A[0:n/2]和A[n/2+1:n-1],分别对这两个子数组单独排序,然后将已排序的两个数组归并成一个含有n个元素的有序数组。(不断地进行二分,直至待排序数组中只剩下一个元素为止,然后不断合并两个排好序的数组段)
void MergeArr(int* a, int begin1, int end1, int begin2, int end2, int* tmp)//归并
{
int left=begin1, right=end2;
int index = begin1;
while (begin1 <= end1 && begin2 <= end2)
{
if (a[begin1] < a[begin2])
{
tmp[index++] = a[begin1++];
}
else
{
tmp[index++] = a[begin2++];
}
}
while (begin1 <= end1)
{
tmp[index++] = a[begin1++];
}
while (begin2 <= end2)
{
tmp[index++] = a[begin2++];
}
for (int i = left; i <= right; ++i)
{
a[i] = tmp[i];
}
}
void _MergeSort(int* a, int left,int right,int*tmp)
{
if (left >= right)
{
return;
}
int mid = (left + right) / 2;
_MergeSort(a, left, mid, tmp);
_MergeSort(a, mid+1,right, tmp);
MergeArr(a, left, mid, mid + 1, right, tmp);
}
void MergeSort(int* a, int n)
{
assert(a);
int* tmp = (int*)malloc(sizeof(int) * n);
_MergeSort(a, 0, n - 1, tmp);
free(tmp);
}