有向图强联通分量+缩点SCC~

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  1 #include <cstdio>
  2 #include <cstring>
  3 
  4  #define MIN(a,b) (a < b ? a : b)
  5 
  6  const int N = 5005;
  7 const int M = 100005;
  8 
  9 struct List
 10 {
 11     int v;
 12     List *next;
 13 } pool[M], *c[N], *g[N], *pp;
 14 
 15 inline void add_edge(int u, int v, List *c[])
 16 {
 17     pp->v = v;
 18     pp->next = c[u];
 19     c[u] = pp++;
 20 }
 21 
 22 int n, m, label, tot, top;
 23 int low[N], dfn[N], num[N], stack[N], hash[N], all_cnt[N], all_n[N], queue[N];
 24 bool used[N];
 25 bool mark[N];
 26 
 27 void SCC_VISIT(int u)
 28 {
 29     low[u] = dfn[u] = label++;
 30     stack[++top] = u;
 31 
 32     for (List *p = c[u]; p; p = p->next)
 33     {
 34         int v = p->v;
 35         if (used[v])     continue;
 36         if (dfn[v] == 0)     SCC_VISIT(v), low[u] = MIN(low[u],low[v]);
 37         else    low[u] = MIN(low[u],dfn[v]);
 38     }
 39 
 40     if (low[u] == dfn[u])
 41     {
 42         ++tot;
 43         do
 44         {
 45             num[stack[top]] = tot;
 46             used[stack[top]] = true;
 47         }
 48         while ( stack[top--] != u );
 49     }
 50 }
 51 
 52 int bfs(int s)
 53 {
 54     int qh = -1;
 55     int qe = 0;
 56     int ret = all_cnt[s];
 57 
 58     memset(used,false,sizeof(used));
 59 
 60     queue[0] = s;
 61     used[s] = true;
 62 
 63     while (qh != qe)
 64     {
 65         int u = queue[++qh];
 66         for (List * p = g[u];p;p = p->next)
 67             if (!used[p->v])
 68             {
 69                 queue[++qe] = p->v;
 70                 used[p->v] = true;
 71                 ret += all_cnt[p->v];
 72             }
 73     }
 74 
 75     return ret - 1;
 76 }
 77 
 78 void SCC(int cas)
 79 {
 80     int i;
 81 
 82     label = 1;
 83     top = -1;
 84     tot = 0;
 85     for (i = 1; i <= n; ++i)    all_n[i] = 0, all_cnt[i] = 0, dfn[i] = 0, mark[i] = false, used[i] = false;
 86     for (i = 1; i <= n; ++i)
 87         if (dfn[i] == 0)   SCC_VISIT(i);
 88 
 89     for (i = 1; i <= n; ++i)    hash[i] = -1;
 90     for (i = 1; i <= tot; ++i)  g[i] = NULL;
 91     for (i = 1; i <= n; ++i)
 92     {
 93         int u = num[i];
 94         for (List *p = c[i]; p; p = p->next)
 95         {
 96             int v = num[p->v];
 97             if (u != v && hash[v] != u)    hash[v] = u, add_edge(u, v, g);
 98         }
 99     }
100 
101     for (int i = 1;i <= n;i++)
102         all_cnt[num[i]]++;
103 
104     int max_n = 0;
105     for (int i = 1;i <= tot;i++)
106     {
107         all_n[i] = bfs(i);
108         if (max_n < all_n[i])
109             max_n = all_n[i];
110     }
111 
112     for (int i = 1;i <= tot;i++)
113         if (all_n[i] == max_n)
114             mark[i] = true;
115 
116     printf("Case %d: %d\n",cas,max_n);
117     max_n = -1;
118     for (int i = 1;i <= n;i++)
119         if (mark[num[i]])
120         {
121             if (max_n != -1) printf(" ");
122             printf("%d",i-1);
123             max_n = 0;
124         }
125     printf("\n");
126 }
127 
128 int main()
129 {
130     int cas;
131     int i, j;
132 
133     scanf("%d",&cas);
134 
135     for (int cc = 1;cc <= cas;cc++)
136     {
137         scanf("%d %d", &n, &m);
138         for (i = 1; i <= n; ++i)   c[i] = NULL;
139         pp = pool;
140 
141         while ( m-- )
142         {
143             scanf("%d %d", &i, &j);
144             add_edge(j + 1, i + 1, c);
145         }
146 
147         SCC(cc);
148     }
149     return 0;
150 }