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| #include <iostream>
#include <algorithm>
#include <memory.h>
#include <string>
#include <queue>
using namespace std;
int map[1000][1000];
int N,M;
int dx[4] = {-1,0,1,0};
int dy[4] = {0,1,0,-1};
int ans = -1;
void BFS()
{
queue<pair<int,int>> q;
for(int i=0;i<N;i++)
for(int j=0;j<M;j++)
if(map[i][j]==1) {
q.push(make_pair(i, j));
}
while(!q.empty())
{
int x=q.front().first;
int y=q.front().second;
q.pop();
for(int i=0;i<4;i++)
{
int next_x = x+dx[i];
int next_y = y+dy[i];
if(next_x<0||next_x>=N||next_y<0||next_y>=M)
continue;
if(map[next_x][next_y]==0)
{
map[next_x][next_y] = map[x][y]+1;
q.push(make_pair(next_x,next_y));
}
}
}
}
int main(void)
{
cin>>M>>N;
for(int i=0;i<N;i++)
for(int j=0;j<M;j++)
cin>>map[i][j];
BFS();
for(int i=0;i<N;i++)
for(int j=0;j<M;j++){
if(map[i][j]==0){
cout<<"-1"<<endl;
return 0;
}
else{
ans = max(ans,map[i][j]);
}
}
cout<<ans-1<<endl;
return 0;
}
|
