Codeforces Round #277.5 (Div. 2)-D_html/css_WEB-ITnose

Question: Find the number of damn rhombuses. Directly enumerate the points at both ends. On average, each point is connected to 20 edges. Use the adjacency list to violently calculate the number of intermediate nodes. Then the number of rhombuses that can be formed by selecting any two intermediate nodes and both ends is r*(r-1)/ 2.

Code:

#include<iostream>#include<cstdio>#include<cmath>#include<map>#include<cstring>#include<algorithm>#define rep(i,a,b) for(int i=(a);i<(b);i++)#define rev(i,a,b) for(int i=(a);i>=(b);i--)#define clr(a,x) memset(a,x,sizeof a)typedef long long LL;using namespace std;const int mod=1e9 +7;const int maxn=3005;const int maxm=30005;int first[maxn],nex[maxm],v[maxm],ecnt,g[maxn][maxn];void add_(int a,int b){    v[ecnt]=b;    nex[ecnt]=first[a];    first[a]=ecnt++;}int main(){    int n,m,x,y;    while(~scanf("%d%d",&n,&m))    {        memset(first,-1,sizeof first);ecnt=0;        memset(g,0,sizeof g);        for(int i=0;i<m;i++)            scanf("%d%d",&x,&y),add_(x,y),g[x][y]=1;        int ans=0;        for(int i=1;i<=n;i++)        {           for(int j=1;j<=n;j++)           if(i!=j){               int r=0;               for(int e=first[i];~e;e=nex[e])               if(g[v[e]][j])r++;               ans+=r*(r-1)/2;           }        }        printf("%d\n",ans);    }    return 0;}

D. Unbearable Controversy of Being

time limit per test

memory limit per test

input

output

Tomash keeps wandering off and getting lost while he is walking along the streets of Berland. It's no surprise! In his home town, for any pair of intersections there is exactly one way to walk from one intersection to the other one. The capital of Berland is very different!

Tomash has noticed that even simple cases of ambiguity confuse him. So, when he sees a group of four distinct intersections a, b, c and d, such that there are two paths from a to c ? one through b and the other one through d, he calls the group a "damn rhombus". Note that pairs (a,?b), (b,?c), (a,?d), (d,?c) should be directly connected by the roads. Schematically, a damn rhombus is shown on the figure below:

Other roads between any of the intersections don't make the rhombus any more appealing to Tomash , so the four intersections remain a "damn rhombus" for him.

Given that the capital of Berland has n intersections and m roads and all roads are unidirectional and are known in advance, find the number of "damn rhombi " in the city.

When rhombi are compared, the order of intersections b and d doesn't matter. of the input contains a pair of integers n, m (1?≤?n?≤?3000,?0?≤?m?≤?30000) ? the number of intersections and roads, respectively. Next m lines list the roads, one per line. Each of the roads is given by a pair of integers ai,?bi (1?≤?ai,?bi?≤?n;ai?≠?bi) ? the number of the intersection it goes out from and the number of the intersection it leads to. Between a pair of intersections there is at most one road in each of the two directions.

Output

Print the required number of "damn rhombi".

Sample test(s)

output

5 41 22 31 44 3

output

4 121 21 31 42 12 32 43 13 23 44 14 24 3

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