[USACO5.3]校园网Network of Schools

 1 #include <bits/stdc++.h>
 2 
 3 using namespace std;
 4 
 5 #define re register
 6 #define rep(i, a, b) for (re int i = a; i <= b; ++i)
 7 #define repd(i, a, b) for (re int i = a; i >= b; --i)
 8 #define maxx(a, b) a = max(a, b);
 9 #define minn(a, b) a = min(a, b);
10 #define LL long long
11 #define inf (1 << 30)
12 
13 inline int read() {
14     int w = 0, f = 1; char c = getchar();
15     while (!isdigit(c)) f = c == ‘-‘ ? -1 : f, c = getchar();
16     while (isdigit(c)) w = (w << 3) + (w << 1) + (c ^ ‘0‘), c = getchar();
17     return w * f;
18 }
19 
20 const int maxn = 100 + 5;
21 
22 vector<int> G[maxn];
23 int pre[maxn], low[maxn], dfs_clock = 0, sccno[maxn], sc = 0;
24 stack<int> s;
25 
26 void dfs(int u) {
27     pre[u] = low[u] = ++dfs_clock;
28     s.push(u);
29     for (register int i = 0; i < G[u].size(); ++i) {
30         register int v = G[u][i];
31         if (!pre[v]) {
32             dfs(v);
33             minn(low[u], low[v]);
34         } else
35         if (!sccno[v]) minn(low[u], pre[v]);
36     }
37     if (pre[u] == low[u]) {
38         sc++; int x = 0;
39         while (x != u) {
40             x = s.top(); s.pop();
41             sccno[x] = sc;
42         }
43     }
44 }
45 
46 int n, b[maxn];
47 
48 int main() {
49     n = read();
50 
51     rep(i, 1, n) {
52         int x;
53         while (x = read()) G[i].push_back(x);
54     }
55 
56     rep(i, 1, n)
57         if (!sccno[i]) dfs(i);
58 
59     int ans = 0;
60     if (sc != 1) {
61         rep(i, 1, n)
62             for (register int j = 0; j < G[i].size(); ++j)
63                 if (sccno[i] != sccno[G[i][j]]) b[sccno[i]] = 1;
64         rep(i, 1, sc) if (!b[i]) ans++;
65         memset(b, 0, sizeof(b));
66         int ans1 = 0;
67         rep(i, 1, n)
68             for (register int j = 0; j < G[i].size(); ++j)
69                 if (sccno[i] != sccno[G[i][j]]) b[sccno[G[i][j]]] = 1;
70         rep(i, 1, sc) if (!b[i]) ans1++;
71         printf("%d\n", ans1);
72         maxx(ans, ans1);
73     } else printf("1\n");
74     printf("%d", ans);
75 
76     return 0;
77 }