UVA - 11324 The Largest Clique (强连通缩点+dp)

 1 #include<bits/stdc++.h>
 2 
 3 using namespace std;
 4 const int N=1e5+10;
 5 int head[N],nxt[N],to[N],ne,n,m;
 6 void addedge(int* head,int u,int v) {
 7     nxt[ne]=head[u],to[ne]=v,head[u]=ne++;
 8 }
 9 int dfn[N],low[N],scc[N],sta[N],nscc,nsta,tot,siz[N];
10 int head2[N];
11 
12 void dfs(int u) {
13     dfn[u]=low[u]=++tot;
14     sta[nsta++]=u;
15     for(int e=head[u]; ~e; e=nxt[e]) {
16         int v=to[e];
17         if(!dfn[v])dfs(v),low[u]=min(low[u],low[v]);
18         else if(!scc[v])low[u]=min(low[u],dfn[v]);
19     }
20     if(low[u]==dfn[u]) {
21         nscc++;
22         for(; !scc[u]; scc[sta[--nsta]]=nscc);
23     }
24 }
25 
26 void getscc() {
27     memset(dfn,0,sizeof dfn);
28     memset(scc,0,sizeof scc);
29     tot=nscc=nsta=0;
30     for(int i=1; i<=n; ++i)if(!dfn[i])dfs(i);
31 }
32 
33 int d[N];
34 
35 int dp(int u) {
36     if(~d[u])return d[u];
37     int x=0;
38     for(int e=head2[u]; ~e; e=nxt[e]) {
39         int v=to[e];
40         x=max(x,dp(v));
41     }
42     return d[u]=siz[u]+x;
43 }
44 
45 int main() {
46     int T;
47     scanf("%d",&T);
48     while(T--) {
49         memset(head,-1,sizeof head);
50         memset(head2,-1,sizeof head2);
51         ne=0;
52         scanf("%d%d",&n,&m);
53         while(m--) {
54             int u,v;
55             scanf("%d%d",&u,&v);
56             addedge(head,u,v);
57         }
58         getscc();
59         memset(siz,0,sizeof siz);
60         for(int u=1; u<=n; ++u)siz[scc[u]]++;
61         for(int u=1; u<=n; ++u) {
62             for(int e=head[u]; ~e; e=nxt[e]) {
63                 int v=to[e];
64                 if(scc[u]!=scc[v])addedge(head2,scc[u],scc[v]);
65             }
66         }
67         memset(d,-1,sizeof d);
68         int ans=0;
69         for(int i=1; i<=nscc; ++i)ans=max(ans,dp(i));
70         printf("%d\n",ans);
71     }
72     return 0;
73 }