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Online practices are the result of a default comparison is the optimal solution for you? Whatever. It should be a title wrong ...
#include<iostream> #include<cstdio> #include<algorithm> #include<cstring> #include<cmath> #include<bitset> using namespace std; typedef long long ll; inline int read() { int x=0,f=1; char ch=getchar(); while(ch<'0'||ch>'9') { if(ch=='-') f=-1; ch=getchar(); } while(ch>='0'&&ch<='9') { x=(x<<1)+(x<<3)+(ch^48); ch=getchar(); } return x*f; } const int N=1007; int n,m,ans; bitset <N> mp[N]; int main() { n=read(),m=read(); int a,b; for(int i=1;i<=m;i++) a=read(),b=read(),mp[a][b]=1; for(int j=1;j<=n;j++) for(int i=1;i<=n;i++) if(mp[i][j]) mp[i]|=mp[j]; ans=n*(n-1)/2; for(int i=1;i<=n;i++) for(int j=1;j<=n;j++) ans-=mp[i][j]; printf("%d\n",ans); return 0; }