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参考：blackcat

bitset 优化floyd

#include <cstdio>#include <cstring>#include <cmath>#include <cstdlib>#include <ctime>#include <iostream>#include <algorithm>#include <sstream>#include <string>#include <vector>#include <queue>#include <stack>#include <map>#include <set>#include <utility>#include <bitset>using namespace std;#define LL long long#define pb push_back#define mk make_pair#define pill pair<int, int>#define mst(a, b)memset(a, b, sizeof a)#define REP(i, x, n)for(int i = x; i <= n; ++i)const int MOD = 1e9 + 7;const int qq = 1e3 + 10;const int INF = 1e9 + 10;int n, m;bitset<qq> mp[qq];void Floyd() {for(int i = 1; i <= n; ++i) {for(int j = 1; j <= n; ++j) {if(mp[j][i])mp[j] |= mp[i];}}}int main(){scanf("%d%d", &n, &m);for(int a, b, i = 1; i <= m; ++i) {scanf("%d%d", &a, &b);mp[a][b] = 1;}Floyd();int ans = 0;for(int i = 1; i <= n; ++i) {for(int j = i + 1; j <= n; ++j) {if(!mp[i][j] && !mp[j][i])ans++;}}printf("%d\n", ans);return 0;}