a62_q2a_pandemic.cpp

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

vector<vector<int>> g;

int main() {
    std::ios_base::sync_with_stdio(false);std::cin.tie(0);
    int r, c, t;std::cin >> r >> c >> t; // 1..r, 1..c
    vector<vector<int>> mtx(r+1, vector<int>(c+1, 0)); // number and visited
    
    int res = 0;
    queue<pair<int, int>> bfs; //node is pair

    for (int i = 1; i <= r; i++) {
        for (int j = 1; j <= c; j++) {
            std::cin >> mtx[i][j];
            if (mtx[i][j] == 1) {
                ++res;
                bfs.push({i, j});
            }
        }
    } 

    while (t--) {
        vector<pair<int, int>> tmp;
        while (! bfs.empty()) {
            int i = bfs.front().first, j = bfs.front().second;
            bfs.pop();
            if (i > 1 && mtx[i-1][j] == 0) {
                mtx[i-1][j] = 1;
                tmp.push_back({i-1, j});
                ++res;
            }
            if (j > 1 && mtx[i][j-1] == 0) {
                mtx[i][j-1] = 1;
                tmp.push_back({i, j-1});
                ++res;
            }
            if (i < r && mtx[i+1][j] == 0) {
                mtx[i+1][j] = 1;
                tmp.push_back({i+1, j});
                ++res;
            }
            if (j < c && mtx[i][j+1] == 0) {
                mtx[i][j+1] = 1;
                tmp.push_back({i, j+1});
                ++res;
            }
        }
        while (tmp.size() > 0) {
            bfs.push(*(tmp.end()-1));
            tmp.pop_back();
        }
    }

    std::cout << res << "\n";
    return 0;
}