Try to understand

#include <bits/stdc++.h>

using namespace std;

vector <int> a(20);
int m, res;

void rec (int n, int sum1, int sum2){
  if (n == m){
      if (abs(sum1 - sum2) < res)
        res = abs(sum1 - sum2);
      return;
    }
  rec(n+1, sum1 + a[n], sum2);
  rec(n + 1, sum1, sum2 + a[n]);
}

int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cin >> m;
  res = 1e6 +1;
  //a.resize(m);
  for (int i = 0; i < m; ++i)
    cin >> a[i];
  rec(0, 0, 0);
  cout << res;

}