1737A - Ela Sorting Books - CodeForces Solution

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

#define fore(i, l, r) for (auto i = (l) - ((l) > (r)); i != (r) - ((l) > (r)); i += 1 - 2 * ((l) > (r)))
#define all(a) begin(a), end(a)
#define sz(a) lli(a.size())
#define pb push_back
#define f first
#define s second

#ifdef LOCAL
#include "../debug.h"
#else
#define debug(...)
#endif

using lli = long long;
using ld = long double;
using ii = pair<lli, lli>;

const lli N = 1e6 + 5;
const lli INF = 4e18 + 5;

lli n, k;
string s;

template <class T>
bool umin(T& a, T b) {
  return (a = min(a, b)) == b;
}

template <class T>
bool umax(T& a, T b) {
  return (a = max(a, b)) == b;
}

void testCase() {
  cin >> n >> k >> s;
  map<char, lli> fr;
  for (char c : s) {
    fr[c]++;
  }
  fore (it, 0, k) {
    lli cnt = 0;
    fore (c, 0, 26) {
      if (fr[c + 'a'] > 0) {
        cnt++;
        fr[c + 'a']--;
        if (cnt == n / k) {
          cout << char(c + 'a' + 1);
          break;
        }
      } else {
        cout << char(c + 'a');
        break;
      }
    }
  }
  cout << '\n';
}

int main() {
  cin.tie(0)->sync_with_stdio(0), cout.tie(0);
  lli tc = 1;
  cin >> tc;
  while (tc--) {
    testCase();
  }
  return 0;
}