uva 12167 - Proving Equivalences（强连通）

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题目链接：uva 12167 - Proving Equivalences

#include <cstdio>
#include <cstring>
#include <vector>
#include <stack>
#include <algorithm>using namespace std;const int maxn = 20005;int N, M, in[maxn], ot[maxn];
int cntlock, cntscc, pre[maxn], low[maxn], sccno[maxn];
vector<int> G[maxn];
stack<int> S;void dfs (int u) {pre[u] = low[u] = ++cntlock;S.push(u);for (int i = 0; i < G[u].size(); i++) {int v = G[u][i];if (!pre[v]) {dfs(v);low[u] = min(low[u], low[v]);} else if (!sccno[v])low[u] = min(low[u], low[v]);}if (low[u] == pre[u]) {cntscc++;while (true) {int x = S.top();S.pop();sccno[x] = cntscc;if (x == u) break;}}
}void findSCC () {cntscc = cntlock = 0;memset(pre, 0, sizeof(pre));memset(sccno, 0, sizeof(sccno));for (int i = 1; i <= N; i++)if (!pre[i]) dfs(i);
}void init () {scanf("%d%d", &N, &M);for (int i = 1; i <= N; i++) G[i].clear();int u, v;while (M--) {scanf("%d%d", &u, &v);G[u].push_back(v);}findSCC();
}int main () {int cas;scanf("%d", &cas);while (cas--) {init ();for (int i = 1; i <= cntscc; i++) in[i] = ot[i] = 1;for (int u = 1; u <= N; u++) {for (int j = 0; j < G[u].size(); j++) {int v = G[u][j];if (sccno[u] != sccno[v])in[sccno[v]] = ot[sccno[u]] = 0;}}int a = 0, b = 0;for (int i = 1; i <= cntscc; i++) {if (in[i]) a++;if (ot[i]) b++;}printf("%d\n", cntscc == 1 ? 0 : max(a, b));}return 0;
}

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