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  1. #include<bits/stdc++.h>
  2.  
  3. using namespace std;
  4.  
  5. int main()
  6. {
  7.     int N,M;
  8.     scanf("%d%d",&N,&M);
  9.  
  10.     int i,j,k;
  11.  
  12.     int mat[N][N];
  13.  
  14.     for(i=0;i<N;i++){for(j=0;j<N;j++){mat[i][j]=0;}}
  15.  
  16.  
  17.  
  18.     for(i=0;i<M;i++)
  19.     {
  20.         int a,b;
  21.         scanf("%d%d",&a,&b);
  22.         a--;b--;
  23.         mat[a][b]=1;
  24.     }
  25.  
  26.     int mat2[N][N];
  27.     for(i=0;i<N;i++){for(j=0;j<N;j++){mat2[i][j]=0;}}
  28.  
  29.     vector<int> Adj[N];
  30.  
  31.     for(i=0;i<N;i++)
  32.     {
  33.         for(j=0;j<N;j++)
  34.         {
  35.             if(mat[i][j])Adj[i].push_back(j);
  36.         }
  37.     }
  38.  
  39.     for(i=0;i<N;i++)
  40.     {
  41.         for(j=0;j<Adj[i].size();j++)
  42.         {
  43.             int v=Adj[i][j];
  44.             for(k=0;k<Adj[v].size();k++)
  45.             {
  46.                 int v2=Adj[v][k];
  47.                 if(v2!=i)
  48.                 {
  49.                     mat[i][v]++;
  50.                 }
  51.             }
  52.         }
  53.     }
  54.  
  55.     long long ans=0;
  56.  
  57.     for(i=0;i<N;i++)
  58.     {
  59.         for(j=0;j<N;j++)
  60.         {
  61.             ans+=(mat2[i][j]*(mat2[i][j]-1))/2;
  62.         }
  63.     }
  64.  
  65.     printf("%d\n",ans);
  66.  
  67.     return 0;
  68. }
Success #stdin #stdout 0s 4376KB
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stdin
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4 12
1 2
1 3
1 4
2 1
2 3
2 4
3 1
3 2
3 4
4 1
4 2
4 3
stdout
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0
https://ideone.com/DyZXrZ
language:
C++14 (gcc 8.3)
created:
4 years ago
visibility:
public

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