Prva

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

int main(){

    vector<string>ans;

    int r, c;
    char d[21][21];
    cin >> r >> c;

    for(int i=0; i<r; i++){
        for(int j=0; j<c; j++){
            cin >> d[i][j];
        }
    }

    for(int i=0; i<=r; i++) d[i][c] = '#';
    for(int i=0; i<=c; i++) d[r][i] = '#';

    string s;
    for(int i=0; i<=r; i++){
        for(int j=0; j<=c; j++){
            if(d[i][j] == '#'){
                if(s.size() > 1) ans.push_back(s);
                s.clear();
            } else {
                s.push_back(d[i][j]);
            }
        }
    }

    for(int j=0; j<=c; j++){
        for(int i=0; i<=r; i++){
            if(d[i][j] == '#'){
                if(s.size() > 1) ans.push_back(s);
                s.clear();
            } else {
                s.push_back(d[i][j]);
            }
        }
    }

    sort(ans.begin(), ans.end());
    cout << ans[0];

    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED