POJ1523 SPF (cut point)

The topic asks for all the cut points of an undirected graph, and the output deletes the cut points and forms several connected components. Using the Tarjan algorithm:

Over Dfs, a depth-first spanning tree is constructed, and the edges in the original graph are divided into two types: the edge of the tree (the edge on the spanning tree) and the anti-ancestor Edge (not the edge on the spanning tree).

By the way, the DFS sequence of each node Dfn[u] and each node can be reached along the atavistic edge of it and its son the smallest DFS order Low[u].

One point is the cut point and only if--

• This point is the root of the spanning tree and has X (x>=2) sub-trees, and the X-connected component is formed after the point is deleted.
• This point is not a root, and its existence x (X>=1) son's low value is less than equal to the DFN value of the point, after the deletion of the point, the formation of x+1 connected components.

1#include <cstdio>2#include <cstring>3#include <algorithm>4 using namespacestd;5 #defineMAXM 1111*1111*26 #defineMAXN 11117 structedge{8     intV,next;9 }EDGE[MAXM];Ten intHead[maxn],ne; One voidAddedge (intUintv) { AEdge[ne].v=v; Edge[ne].next=head[u]; head[u]=ne++; - } - intDN,DFN[MAXN],LOW[MAXN],SON[MAXN]; the voidDfsintu) { -dfn[u]=low[u]=++DN; -      for(intI=head[u]; i!=-1; I=Edge[i].next) { -         intv=edge[i].v; +         if(Dfn[v]) { -low[u]=min (low[u],dfn[v]); +             Continue; A         } at Dfs (v); -         if(u==1) ++Son[u]; -         Else if(Low[v]>=dfn[u]) + +Son[u]; -low[u]=min (low[u],low[v]); -     } - } in BOOLoutput () { -     BOOLflag=0; to     if(son[1]>=2) printf ("SPF node 1 leaves%d subnets\n", son[1]), flag=1; +      for(intu=2; u<= +; ++u) { -         if(Son[u]) printf ("SPF node%d leaves%d subnets\n", u,son[u]+1), flag=1; the     } *     returnFlag; $ }Panax Notoginseng intMain () { -     intu,v,t=0; the      for(;;) { +         BOOLflag=1; ANe=0; thememset (head,-1,sizeof(head)); +          while(~SCANF ("%d", &u) &&u) { -scanf"%d",&v); $ Addedge (u,v); Addedge (v,u); $flag=0; -         } -         if(flag) Break; thedn=0; -memset (DFN,0,sizeof(DFN));WuyiMemset (son,0,sizeof(son)); theDfs1); -printf"Network #%d\n",++t); Wu         if(!output ()) puts ("No SPF Nodes"); -Putchar ('\ n'); About     } $     return 0; -}

POJ1523 SPF (cut point)