Вирусы

#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <queue>
using namespace std;

int main() {

    std::ifstream fin("input.txt");
    std::ofstream fout("output.txt");

    short n, m, k;
    fin >> n >> m >> k;

    vector<vector<bool>> map(n, vector<bool> (m, false));

    queue<int> qi, qj;
    int vi, vj;
    vector<int> di = { 0, 0, 1, -1 };
    vector<int> dj = { 1, -1, 0, 0 };
    int max = 0;
    for (int i = 0; i < k; ++i) {
        fin >> vi >> vj;
        vi--; vj--;
        qi.push(vi);
        qj.push(vj);
        map[vi][vj] = true;
    }

    int r = k, sr = 0;
        while (!qi.empty()) {

            vi = qi.front();
            vj = qj.front();
            qi.pop();
            qj.pop();

            for (int i = 0; i < 4; ++i) {
                vi += di[i];
                vj += dj[i];
                if (vi >= 0 && vi < n && vj >= 0 && vj < m) {
                    if (map[vi][vj] == false) {
                        qi.push(vi);
                        qj.push(vj);
                        map[vi][vj] = true;
                        sr++;
                    }
                }
                vi -= di[i];
                vj -= dj[i];
            }
            r--;
            if (r == 0) {
                max++;
                swap(r, sr);
            }
        }
    fout << max;

    return 0;

}