DS contest 6 problem F-E

//Bismillahir Rahman-ir Rahim
#include <bits/stdc++.h>
using namespace std;
#define debug(x) cout << '>' << #x << " : " << x << endl;
#define all(c) c.begin(), c.end()
#define F first
#define S second
typedef unsigned long long ull;
typedef long long ll;

int dx[] = {1, -1, 0, 0};
int dy[] = {0, 0, 1, -1};

char mat[5000][5000];

bool valid(int x, int y, int n, int m){
    if(x >= 0 and x <= n and y >= 0 and y <= m and mat[x][y] != '#' and mat[x][y] != 'X') return 1;
    return 0;
}

int main() {

    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);

    int n, m, d;
    cin >> n >> m >> d;

    for(int i = 0; i < n; i++){
        string str;
        cin >> str;
        for(int j = 0; j < m; j++){
            mat[i][j] = str[j];
        }
    }
    bool br = 0;
    for(int i = 0; i < n; i++){
        for(int j = 0; j < m; j++){
            if(d <= 0){
                br = 1;
                break;
            }
            if(mat[i][j] == '.'){
                mat[i][j] = 'X';
                bool ok = 1;
                //pair <int,int> cur = {i, j};

                //go to the neighbours of i ,j

                for(int k = 0; k < 4; k++){
                    if(valid(i+dx[k], j+dy[k], n, m)){
                        // check if it's blocked
                        int curi = i+dx[k], curj = j+dy[k];
                        bool blocked = 1;
                        for(int l = 0; l < 4; l++){
                            if(valid(curi + dx[l], curj + dy[l], n, m)){
                                blocked = 0;
                                break;
                            }
                        }
                        if(blocked){
                            ok = 0;
                            break;
                        }
                    }
                }


                if(!ok){
                    mat[i][j] = '.';
                }
                else{
                    d--;
                }
            }
        }
        if(br) break;
    }
    for(int i = 0; i < n; i++){
        for(int j = 0; j < m; j++){
            cout << mat[i][j];
        }
        cout << endl;
    }
    cout << endl;

    return 0;
}