[USACO5.3]校园网Network of Schools
题目传送门
$Tarjan$缩点，不多说。
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 }
