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  • hdu 2767 Proving Equivalences 强连通

    #include<cstdio>
    #include<algorithm>
    #include<vector>
    #include<cstring>
    #include<stack>
    using namespace std;
    
    const int maxn = 20000 + 10;
    
    vector<int> G[maxn], G2[maxn];
    vector<int> S;
    int vis[maxn], sccno[maxn], scc_cnt;
    
    void dfs1(int u) 
    {
        if(vis[u]) return;
        vis[u] = 1;
        for(int i = 0; i < G[u].size(); i++) dfs1(G[u][i]);
        S.push_back(u);
    }
    
    void dfs2(int u) 
    {
        if(sccno[u]) return;
        sccno[u] = scc_cnt;
        for(int i = 0; i < G2[u].size(); i++) dfs2(G2[u][i]);
    }
    
    void find_scc(int n) 
    {
        scc_cnt = 0;
        S.clear();
        memset(sccno, 0, sizeof(sccno));
        memset(vis, 0, sizeof(vis));
        for(int i = 0; i < n; i++) dfs1(i);
        for(int i = n-1; i >= 0; i--)
        if(!sccno[S[i]]) { scc_cnt++; dfs2(S[i]); }
    }
    
    int in0[maxn], out0[maxn];
    
    int main() 
    {
        int T, n, m;
        scanf("%d", &T);
        while(T--) 
        {
            scanf("%d%d", &n, &m);
            for(int i = 0; i < n; i++) { G[i].clear(); G2[i].clear(); }
            for(int i = 0; i < m; i++) 
            {
                int u, v;
                scanf("%d%d", &u, &v); u--; v--;
                G[u].push_back(v); G2[v].push_back(u);
            }
    
            find_scc(n);
    
            for(int i = 1; i <= scc_cnt; i++) in0[i] = out0[i] = 1;
            for(int u = 0; u < n; u++)
            for(int i = 0; i < G[u].size(); i++) 
            {
                int v = G[u][i];
                if(sccno[u] != sccno[v]) in0[sccno[v]] = out0[sccno[u]] = 0;
            }
            int a = 0, b = 0;
            for(int i = 1; i <= scc_cnt; i++) 
            {
                if(in0[i]) a++;
                if(out0[i]) b++;
            }
            int ans = max(a, b);
            if(scc_cnt == 1) ans = 0;
            printf("%d
    ", ans);
        }
        return 0;
    }


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  • 原文地址:https://www.cnblogs.com/vermouth/p/3710186.html
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