Ruudukko

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

int n;
string m[500];
string b[500][500];
string bestCol = "";

void sett(int x, int y) {
  if(x == 0) {
    b[y][x] = b[y - 1][x] + m[y][x]; 
  }
  else if(y == 0) {
    b[y][x] = b[y][x - 1] + m[y][x];
  } else {
    b[y][x] = min(b[y - 1][x], b[y][x - 1]) + m[y][x];
  }
}

int main() {
  cin.sync_with_stdio(0);
  cin >> n;
  for(int y = 0; y < n; ++y) {
    cin >> m[y];
  }
  b[0][0] = m[0][0];
  for(int xs = 1; xs < 2 * n - 1; ++xs) {
    int d = max(0, xs - (n - 1));
    for(int ys = d; ys <= min(xs, n - 1); ++ys) {
      int x = xs - ys;
      int y = ys;
      //   cout << xs << " " << x << " " << y << "\n";
      sett(x, y);
    }
    string minStr = "";
    minStr.push_back('Z' + 1);
    for(int ys = d; ys <= min(xs, n - 1); ++ys) {
      int x = xs - ys;
      int y = ys;
      minStr = min(minStr, b[y][x]);
    }
    for(int ys = d; ys <= min(xs, n - 1); ++ys) {
      int x = xs - ys;
      int y = ys;
      if(b[y][x] > minStr) {
	b[y][x].clear();
	b[y][x].push_back('Z' + 2);
      } else {
	b[y][x].clear();
	b[y][x].push_back(m[y][x]);
      }
    }
    //  cout << "minStr: '" << minStr << "'\n";
    bestCol += minStr.back();
  }
  cout << m[0][0] << bestCol << "\n";
}

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