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  1. #include <iostream>
  2. #include <cstring>
  3. #include <stack>
  4. #define maxn 1000
  5. using namespace std;
  6. stack <int> s;
  7. char g[maxn][maxn];
  8. bool used[maxn][maxn];
  9. int n,m, max_d=0, root_x=0, root_y=0;
  10. void dfs(int cx,int cy, int h){
  11.     s.push(cx);
  12.     s.push(cy);
  13.     s.push(h);
  14.     while(!s.empty()){
  15.         int h=s.top();
  16.         s.pop();
  17.         int y=s.top();
  18.         s.pop();
  19.         int x=s.top();
  20.         s.pop();
  21.         used[x][y]=true;
  22.     if(h>max_d)
  23.         max_d=h,root_x=x,root_y=y;
  24.     if(x>0 && g[x-1][y]=='.' && !used[x-1][y])
  25.         s.push(x-1),s.push(y),s.push(h+1);
  26.     if(y>0 && g[x][y-1]=='.' && !used[x][y-1])
  27.         s.push(x),s.push(y-1),s.push(h+1);
  28.     if(x<n-1 && g[x+1][y]=='.' && !used[x+1][y])
  29.         s.push(x+1),s.push(y),s.push(h+1);
  30.     if(y<m-1 && g[x][y+1]=='.' && !used[x][y+1])
  31.        s.push(x),s.push(y+1),s.push(h+1);
  32.     }
  33. }
  34. int main(){
  35.     cin>>m>>n;
  36.     for(int i=0; i<n; ++i){
  37.         cin>>g[i];
  38.         for(int j=0; j<m; ++j)
  39.              used[i][j]=false;
  40.     }
  41.     for(int i=0; i<n; ++i){
  42.         for(int j=0; j<m; ++j)
  43.             if(g[i][j]=='.' && !used[i][j]){
  44.                 dfs(i,j,0);
  45.                 for(int k=0;k<n;++k)
  46.                     for(int l=0;l<m;++l)
  47.                         used[k][l]=0;
  48.                 dfs(root_x,root_y,0);
  49.         }
  50.     }
  51.     cout<<max_d<<endl;
  52.     return 0;
  53. }
Success #stdin #stdout 0s 18016KB
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https://ideone.com/LFOEF3
language:
C++ (gcc 8.3)
created:
6 years ago
visibility:
public

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