Inversion counting using Merge Sort

#include "bits/stdc++.h"
using namespace std;
const int N = 65537 + 4;
vector < long long > v(N);
long long merge(int, int, int, int);
long long merge_sort(int l, int r) {
	int mid = (l+r) >> 1;
	long long lInver = 0, rInver = 0, mergeInver = 0;
	if (l != mid) {
		lInver = merge_sort(l, mid);
	}
	if (r != mid+1) {
		rInver = merge_sort(mid+1, r);
	}
	if (r != l) {
 		mergeInver = merge(l, mid, mid+1, r);
 	}
 	return mergeInver + lInver + rInver;
}

long long merge(int l1, int r1, int l2, int r2) {
	vector < long long > temp(r2-l1+1);
	long long tInver = 0;
	int i = l1, j = l2, k = 0;
	while (i <= r1 && j <= r2) {
		if (v[i] <= v[j]) {
			temp[k] = v[i];
			++i;
		}
		else {
			temp[k] = v[j];
			++j;
			tInver += l2 - i;
		}
		++k;
	}
	while (i <= r1) {
		temp[k++] = v[i++];
	}
	while (j <= r2) {
		temp[k++] = v[j++];
	}
	for (int k = 0, i = l1; i <= r2; ++i) {
		v[i] = temp[k++];
	}
	return tInver;
}

int main() {
	int t = 1;
	// cin >> t;
	while (t--) {
		int n;
		cin >> n;
		// n = 1e7;
		for (int i = 0; i < n; ++i) {
			cin >> v[i];
		}
		cout << merge_sort(0, n-1) << '\n';
	}
}