Ruudukko

#include <iostream>
#include <vector>
using namespace std;

string s[511];
bool k[501][501];


int main(){
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n;
  cin >> n;
  for (int i=0; i<n; ++i) cin >> s[i];
  k[0][0]=true;
  cout << s[0][0];
  for (int i=0; i<n*2-2; ++i){
    char m='Z'+1;
    for (int x=0; x<n; ++x){
      int y=i-x;
      if (y<0 || y>=n || !k[y][x]) continue;
      m=min(m, min(x<n-1?s[y][x+1]:m, y<n-1?s[y+1][x]:m));
    }
    cout <<  m;
    for (int x=0; x<n; ++x){
      int y=i-x;
      if (y<0 || y>=n || !k[y][x]) continue;
      if (x<n-1) if (s[y][x+1]==m) k[y][x+1]=true;
      if (y<n-1) if (s[y+1][x]==m) k[y+1][x]=true;
    }
  }
  cout << 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