Ruudukko

#include <bits/stdc++.h>
using namespace std;
int di[] {1, 0};
int dj[] {0, 1};
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int n;
  cin >> n;
  string g[n];
  for (int i = 0; i < n; ++i) {
    cin >> g[i];
  }
  string ans{g[0][0]};
  set<pair<int, int>> q, nq;
  q.emplace(0, 0);
  for (int t = 0; t < n + n - 2; ++t) {
    nq.clear();
    char b = 'Z';
    for (auto [i, j] : q) {
      for (int k = 0; k < 2; ++k) {
        int ni = i + di[k];
        int nj = j + dj[k];
        if (ni >= n) continue;
        if (nj >= n) continue;
        b = min(b, g[ni][nj]);
      }
    }
    ans += b;
    for (auto [i, j] : q) {
      for (int k = 0; k < 2; ++k) {
        int ni = i + di[k];
        int nj = j + dj[k];
        if (ni >= n) continue;
        if (nj >= n) continue;
        if (g[ni][nj] == b) {
          nq.emplace(ni, nj);
        }
      }
    }
    q = nq;
  }
  cout << ans << endl;
}

Test 1

Group: 1

Verdict: ACCEPTED

Test 2

Group: 1

Verdict: ACCEPTED

Test 3

Group: 1

Verdict: ACCEPTED

Test 4

Group: 1

Verdict: ACCEPTED

Test 5

Group: 1

Verdict: ACCEPTED

Test 6

Group: 2

Verdict: ACCEPTED

Test 7

Group: 2

Verdict: ACCEPTED

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 3

Verdict: ACCEPTED

Test 12

Group: 3

Verdict: ACCEPTED

Test 13

Group: 3

Verdict: ACCEPTED

Test 14

Group: 3

Verdict: ACCEPTED

Test 15

Group: 3

Verdict: ACCEPTED