ACM-ICPC 2017 南宁赛区现场赛 M. The Maximum Unreachable Node Set

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 #define ll long long
 4 #define ull unsigned long long
 5 #define mst(a,b) memset((a),(b),sizeof(a))
 6 #define mp(a,b) make_pair(a,b)
 7 #define pi acos(-1)
 8 #define pii pair<int,int>
 9 #define pb push_back
10 const int INF = 0x3f3f3f3f;
11 const double eps = 1e-6;
12 const int MAXN = 1e5 + 10;
13 const int MAXM = 2e6 + 10;
14 
15 int n,m;
16 int g[110][110],fa[110];
17 bool vis[110];
18 
19 bool dfs(int u) {
20     for(int i = 1; i <= n; i++) {
21         if(g[u][i] && !vis[i]) {
22             vis[i] = true;
23             if(fa[i] == 0 || dfs(fa[i])) {
24                 fa[i] = u;
25                 return true;
26             }
27         }
28     }
29     return false;
30 }
31 
32 int main() {
33 #ifdef local
34     freopen("data.txt", "r", stdin);
35 //    freopen("data.txt", "w", stdout);
36 #endif
37     int t;
38     scanf("%d",&t);
39     while(t--) {
40         scanf("%d%d",&n,&m);
41         for(int i = 1; i <= n; i++) {
42             fa[i] = 0;
43             for(int j = 1; j <= n; j++) g[i][j] = 0;
44         }
45         while(m--) {
46             int u,v;
47             scanf("%d%d",&u,&v);
48             g[u][v] = 1;
49         }
50         for(int k = 1; k <= n; k++)
51             for(int i = 1; i <= n; i++)
52                 for(int j = 1; j <= n; j++)
53                     g[i][j] |= g[i][k] & g[k][j];
54         int res = 0;
55         for(int i = 1; i <= n; i++) {
56             mst(vis, 0);
57             if(dfs(i)) res++;
58         }
59         printf("%d\n",n - res);
60     }
61     return 0;
62 }