归并排序

void Merge(int a[], int left, int mid, int right)
{
assert(a);
int* tmp = new int[right - left + 1]();
int index = 0;

int begin1 = left, end1 = mid;
int begin2 = mid + 1, end2 = right;
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++];
}
memcpy(a + left, tmp, sizeof(int)*(index));
delete[]tmp;
}

void MergeSort(int a[], int left, int right)
{
if (left < right)
{
int mid = left + (right - left) / 2;
MergeSort(a, left, mid);
MergeSort(a, mid + 1, right);
Merge(a, left, mid, right);
}
}

void merge_sort(int a[], int size)
{
assert(a);
for (int gap = 1; gap < size; gap *= 2)//gap为子数组中元素的个数
{
int i = 0;
for (; i + 2 * gap - 1 < size; i += 2 * gap)
{
Merge(a, i, i + gap - 1, i + 2 * gap - 1);
}
if (i + gap - 1 < size-1)
{
Merge(a, i, i + gap - 1, size - 1);
}
}

}