有向无环图的最小路径覆盖 = 顶点数- 最大匹配

#include <queue>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;

const int maxn = 150;
int g[maxn][maxn];
int n, m;
int link[maxn];
bool used[maxn];
bool dfs(int u)
{
    for(int v=1; v<=n; ++v)
        if(g[u][v]&&!used[v]) {
            used[v] = true;
            if( link[v]==-1 || dfs(link[v])) {
                link[v] = u;
                return true;
            }
        }
    return false;
}

int hungary()
{
    int res = 0;
    memset(link, -1, sizeof link );
    for(int i=1; i<=n; ++i) {
        memset(used, 0, sizeof used );
        if(dfs(i)) res++;
    }
    return res;
}
int main()
{
    int u, v, t;
    scanf("%d", &t);
    while(t--) {
        scanf("%d%d", &n, &m);
        memset(g, 0, sizeof g );
        for(int i=1; i<=m; ++i) {
            scanf("%d%d", &u, &v);
            g[u][v] = 1;
        }

        int cnt = hungary();
        printf("%d\n", n-cnt);
    }
    return 0;
}

hdu1151 Air Raid，DAG图的最小路径覆盖