二分图 : 最小路径重复点覆盖

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最小路径重复点覆盖

#include <bits/stdc++.h>
using namespace std;
#define IO ios::sync_with_stdio(false);cin.tie(0); cout.tie(0)
inline int lowbit(int x) { return x & (-x); }
#define ll long long
#define ull unsigned long long
#define pb push_back
#define PII pair<int, int>
#define x first
#define y second
#define inf 0x3f3f3f3f
const int N = 210, M = 30010;
int n, m;
int match[N];
bool d[N][N], st[N];

bool find(int x) {
    for (int i = 1; i <= n; ++i) 
        if (d[x][i] && !st[i]) {
            st[i] = 1;
            int t = match[i];
            if (t == 0 || find(t)) {
                match[i] = x;
                return true;
            }
        }
    return false;
}

int main() {
    IO;
    cin >> n >> m;
    while (m--) {
        int a, b;
        cin >> a >> b;
        d[a][b] = 1;
    }
    for (int k = 1; k <= n; ++k)
        for (int i = 1; i <= n; ++i)
            for (int j = 1; j <= n; ++j)
                d[i][j] |= d[i][k] & d[k][j];
    int res = 0;
    for (int i = 1; i <= n; ++i) {
        memset(st, 0, sizeof st);
        if (find(i)) res++;
    }
    cout << n - res << '\n';
    return 0;
}