题意
Sol
显然如果题目什么都不说的话需要\(\frac{n * (n - 1)}{2}\)个相对关系
然后求一下传递闭包减掉就行了
#include<bits/stdc++.h>
using namespace std;
const int MAXN = 1001;
inline int read() {
char c = getchar(); int x = 0, f = 1;
while(c < '0' || c > '9') {if(c == '-') f = -1; c = getchar();}
while(c >= '0' && c <= '9') x = x * 10 + c - '0', c = getchar();
return x * f;
}
int N, M;
bitset<MAXN> f[MAXN];
int main() {
N = read(); M = read();
for(int i = 1; i <= M; i++) {
int x = read(), y = read();
f[x][y] = 1;
}
for(int k = 1; k <= N; k++)
for(int i = 1; i <= N; i++)
if(f[i][k]) f[i] = f[i] | f[k];
int ans = N * (N - 1) / 2;
for(int i = 1; i <= N; i++) ans -= f[i].count();
cout << ans;
return 0;
}