ZombieMatrix.cpp

#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize ("-O3")

void bfs(){
    vector<int> dir={-1,0,1,0,-1};
    int n,m;
    cin>>n>>m;
    vector<vector<int>> board(n,vector<int>(m));
    queue<pair<int,int>> q;
    for(int i=0;i<n;i++){
        for(int j=0;j<m;j++){
            cin>>board[i][j];
            if(board[i][j]==1){
                q.push({i,j});
            }
        }
    }
    int ans = -1;
    while(!q.empty()){
        int size = q.size();
        while(size--){
            auto top = q.front();
            q.pop();
            for(int i=0; i<4; i++){
                int nr = top.first + dir[i];
                int nc = top.second + dir[i+1];
                if(0<=nr && nr<n && 0<=nc && nc<m && board[nr][nc]==0){
                    board[nr][nc] = 1;
                    q.push({nr,nc});
                }
            }
        }
        ans++;
    }
    if(ans==-1){
        cout<<0<<"\n";
        return;
    }
    cout<<ans<<"\n";
    return;
}

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(NULL); cout.tie(NULL);
    bfs();
    return 0;
}