C++でマージソートを書いてみた

void merge(int n[], int left, int mid, int right)
{
    int num = right - left;
    int *tmp = new int[num];

    int iw = 0;
    int il = left;
    int ir = mid;

    while (il < mid && ir < right)
    {
        if (n[il] <= n[ir])
        {
            tmp[iw++] = n[il++];
        } else {
            tmp[iw++] = n[ir++];
        }
    }

    while (il < mid) tmp[iw++] = n[il++];
    while (ir < right) tmp[iw++] = n[ir++];

    for (int i=0; i<num; i++) n[left + i] = tmp[i];

    delete[] tmp;
}


void merge_sort_sub(int n[], int left, int right)
{
    if (right - left <= 1) return;

    int mid = left + (right - left) / 2;
    merge_sort_sub(n, left, mid);
    merge_sort_sub(n, mid, right);

    merge(n, left, mid, right);
}


void merge_sort(int n[], int len)
{
    merge_sort_sub(n, 0, len);
}