the number of swaps required in selection sort

1#include <bits/stdc++.h>
2using namespace std;
3 
4typedef long long ll;
5 
6ll a[111111], tmp[111111], ans;
7 
8void merge_sort(ll a[], ll b[], ll lo, ll hi)
9{
10    ll i, j, k;
11 
12    if (lo >= hi)
13        return;
14 
15    ll mid = (lo + hi) / 2;
16 
17    merge_sort(a, b, lo, mid);
18    merge_sort(a, b, mid + 1, hi);
19 
20    i = lo;
21    j = mid + 1;
22 
23    for (k = lo; k <= hi; k++)
24        if (j > hi)
25            b[k] = a[i++];
26        else if (i > mid)
27            b[k] = a[j++];
28        else if (a[i] <= a[j])
29            b[k] = a[i++];
30        else
31        {
32            b[k] = a[j++];
33            ans += mid - i + 1;
34        }
35 
36    for (i = lo; i <= hi; i++)
37        a[i] = b[i];
38}
39 
40int main(void)
41{
42    ll t;
43 
44    scanf("%lld", &t);
45 
46    while (t--)
47    {
48        ll n, i;
49 
50        scanf("%lld", &n);
51        for (i = 1; i <= n; i++)
52            scanf("%lld", &a[i]);
53 
54        ans = 0;
55        merge_sort(a, tmp, 1, n);
56 
57        printf("%lld\n", ans);
58    }
59    return 0;
60}