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  1.  
  2.  
  3. #include <bits/stdc++.h>
  4. using namespace std;
  5. #define MAX 100009
  6. bool check[MAX]={false};
  7. int total=0;
  8. int dfs(vector<int> v[],int root)
  9. {
  10.     int m,m1=-1,m2=-1;
  11.     check[root]=1;
  12.     for(int i=0;i<v[root].size();i++)
  13.     {
  14.         if(!check[v[root][i]]){
  15.             m = dfs(v,v[root][i]);
  16.             if(m>=m1)
  17.             {
  18.                 m2= m1;
  19.                 m1 = m;
  20.             }
  21.             else if(m>m2)
  22.                 m2=m;
  23.         }
  24.     }
  25.     total = max(total , m1+m2+2);
  26.     return (m1 + 1);
  27. }
  28. int main()
  29. {
  30.     int n,a,b;
  31.     cin>>n;
  32.     vector<int> v[n+9];
  33.     for(int i=0;i<n-1;i++){
  34.         scanf("%d%d",&a,&b);
  35.         v[a].push_back(b);
  36.         v[b].push_back(a);
  37.     }
  38.     dfs(v,1);
  39.     cout<<total<<endl;
  40. }
  41.  
Success #stdin #stdout 0s 4176KB
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https://ideone.com/ZZncXl
language:
C++ (gcc 8.3)
created:
4 years ago
visibility:
public

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