bfs.cpp

#include<bits/stdc++.h>
#define ll long long int
using namespace std;
ll dx[4] = {0, 1, 0, -1};
ll dy[4] = {1, 0, -1, 0};
int main()
{
    ios_base:: sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
    // ll t;
    // cin>>t;
    // while(t--)
    {
        ll i, j, k, n, m, cnt = 0, sum = 0;
        cin >> n >> m >> k;
        string s[n];
        for (i = 0; i < n; i++) {
            cin >> s[i];
        }
        vector<pair<ll, ll>> ans;
        pair<ll, ll> start;
        for (i = 0; i < n; i++) {
            for (j = 0; j < m; j++) {
                if (s[i][j] == '.') {
                    start = {i, j};
                    break;
                }
            }
            if (s[i][j] == '.') {
                break;
            }
        }
        ll vis[n][m];
        memset(vis, 0, sizeof(vis));
        queue<pair<ll, ll>> Q;
        Q.push(start);
        ans.push_back(start);
        vis[start.first][start.second] = 1;
        while (!Q.empty()) {
            pair<ll, ll> cur = Q.front();
            Q.pop();
            ll x = cur.first;
            ll y = cur.second;
            for (i = 0; i < 4; i++) {
                ll xx = x + dx[i];
                ll yy = y + dy[i];
                if (xx >= 0 && xx < n && yy >= 0 && yy < m && s[xx][yy] == '.' && !vis[xx][yy]) {
                    Q.push({xx, yy});
                    cout << xx << " " << yy << '\n';
                    vis[xx][yy] = 1;
                    ans.push_back({xx, yy});
                }
            }
        }
        reverse(ans.begin(), ans.end());
        for (i = 0; i < k; i++) {
            s[ans[i].first][ans[i].second] = 'X';
        }
        for (i = 0; i < n; i++) {
            for (j = 0; j < m; j++) {
                cout << s[i][j];
            }
            cout << '\n';
        }
    }
}