[Link] https://www.acmicpc.net/problem/2638
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#include <algorithm>
#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <cstring>
// #include <bits/stdc++.h>
using namespace std;
#define for0(i, n) for(int i = 0; i < n; i++)
#define for1(i, n) for(int i = 1; i < n; i++)
#define fori(s, e) for(int i = s; i < e; i++)
#define ll long long
#define endl "\n"
#define nulls '\0'
#define dkdk " "
const int MAX = 5e5 + 1;
int n, m, time;
bool mm[100][100];
bool visit[100][100];
int deg[100][100];
int di[4] = { -1, 0, 1, 0 };
int dj[4] = { 0, 1, 0, -1 };
queue<pair<int,int>> q;
void bfs(int i, int j) {
// q = {}; // clear;
if(visit[i][j]) return;
q.push({ i, j });
while(!q.empty()) {
pair<int, int> p = q.front(); q.pop();
int ci = p.first, cj = p.second;
if(visit[ci][cj]) continue;
visit[ci][cj] = true;
for0(k, 4) {
int ai = ci + di[k], aj = cj + dj[k];
if(ai < 0 || aj < 0 || ai>= n || aj >= m) continue;
if(visit[ai][aj]) continue;
if(mm[ai][aj]) { deg[ai][aj]++; continue; }
q.push({ ai, aj });
}
}
}
void solve() {
while(true) {
bool cheese = false;
for0(i, n) for0(j, m) if(mm[i][j]) { cheese = true; break; }
if(cheese == false) break;
for0(i, n) for0(j, m) { visit[i][j] = false; deg[i][j] = 0; }
for0(i, n) { bfs(i, 0); bfs(i, m-1); }
for0(j, m) { bfs(0, j); bfs(n-1, j); }
for0(i, n) for0(j, m) if(deg[i][j] >= 2) mm[i][j] = false;
time++;
}
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> m;
for0(i, n) for0(j, m) cin >> mm[i][j];
solve();
cout << time;
return 0;
}