Help me find testcases where my code for SOLVEMORE is failing

help
,
1

So, here’s my code for SOLVEMORE from STARTERS 78.
This is the basic idea of what I’m doing.
Take sum of ai and bi, store it in ci {si, i}. ci is a vector of pair<ll, int>, which stores sum and index.
Then, sort c.
Find cumulative sum for c.
Using std::upper_bound, find idx for which ci > k.
Now, we find if there is an ai, which when added to ci-1 <=k
We do this by adding ci.second, that is original indices involved, and are part of problems solved to a set.
We iterate over a, if there’s an a s.t c[idx-1] + a[i] <= k and i is not in set, then we increase our answer.

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;

int main() {
  int t;
  cin >> t;
  while (t--) {
    ll n, k, i;
    cin >> n >> k;
    vector<ll> a(n), b(n);
    vector<pair<ll, int>> c(n);
    for (i = 0; i < n; i++) cin >> a[i];
    for (i = 0; i < n; i++) {
      cin >> b[i];
      c[i].first = a[i] + b[i];
      c[i].second = i;
    }
    sort(c.begin(), c.end());
    for (i = 1; i < n; i++) c[i].first += c[i - 1].first;
    auto idx = distance(c.begin(),
                        upper_bound(c.begin(), c.end(), make_pair(k, INT_MIN)));
    unordered_set<int> us;
    for (i = 0; i < idx; i++) {
      us.emplace(c[i].second);
    }
    ll ans = idx;
    if (idx - 1 >= 0) {
      for (i = 0; i < n; i++) {
        if (!us.count(i) && a[i] + c[idx - 1].first <= k) {
          ans++;
          break;
        }
      }
    }
    std::cout << ans << endl;
  }
  return 0;
}