下面程序的 Merge_Sort 函数时间复杂度为（    ）。

void Merge(int a[], int left, int mid, int right) {

int temp[right - left + 1];

int i = left;

int j = mid + 1;

int k = 0;

while (i <= mid && j <= right) {

if (a[i] < a[j])

temp[k++] = a[i++]; else

temp[k++] = a[j++];

}

while (i <= mid)

temp[k++] = a[i++];

while (j <= right)

temp[k++] = a[j++];

for (int m = left, n = 0; m <= right; m++, n++)

a[m] = temp[n];

}

void Merge_Sort(int a[], int left, int right) {

if (left == right)

return;

int mid = (left + right) / 2;

Merge_Sort(a, left, mid);

Merge_Sort(a, mid + 1, right);

Merge(a, left, mid, right);

}