POJ 2762 going from U-V or from V to u? "Strong Connectivity topology sequencing"

Give n points, M edge, ask whether any two points u,v, whether meet u can reach V, or V can reach U

When you write, think of a pinch, and then judge if you can sort the topology.

But--wa---

Then I read the puzzle.

Http://edward-mj.com/archives/27

According to the Purple book, if there is a forward ring in the diagram, there is no topological ordering, and conversely there is

So the above image is for topological sequencing.

But because U,v's penetration is not 0,u,v between

So the graph after the end of the contraction point should be satisfied is a long chain.

1#include <cstdio>2#include <cstring>3#include <iostream>4#include <algorithm>5#include <stack>6#include <queue>7#include <vector>8 using namespacestd;9 Ten Const intMAXN =20005; One intFIRST[MAXN]; A intLOW[MAXN],PRE[MAXN],SC[MAXN]; - int inch[MAXN],DOUT[MAXN]; - intn,m; the intEcnt,scnt,dfs_clock; -stack<int>S; -  -vector<int>G[MAXN]; + intC[MAXN]; - intANS[MAXN]; +  A structedge{ at     intV,next; -}e[3*MAXN]; -  - voidinit () { -ECNT =0; -memset (first,-1,sizeof(first)); inMemsetinch,0,sizeof(inch)); -memset (Dout,0,sizeof(dout)); to } +  - voidAddedges (intUintv) { theE[ECNT].V =v; *E[ecnt].next =First[u]; $First[u] = ecnt++;Panax Notoginseng } -  the voidDfsintu) { +Low[u] = Pre[u] = + +Dfs_clock; A s.push (u); the      for(inti = First[u];~i;i =E[i].next) { +         intv =e[i].v; -         if(!Pre[v]) { $ Dfs (v); $Low[u] =min (low[u],low[v]); -         } -         Else if(!sc[v]) low[u] =min (low[u],pre[v]); the     } -     if(Pre[u] = =Low[u]) {Wuyiscnt++; the          for(;;) { -             intx =S.top (); S.pop (); WuSC[X] =scnt; -             if(x = = u) Break; About         } $     } - } -  - voidFIND_SCC () { A      while(!S.empty ()) S.pop (); +memset (Low,0,sizeof(low)); memset (PRE,0,sizeof(pre)); theMemset (SC,0,sizeof(SC)); -Dfs_clock = SCNT =0; $      for(inti =1; I <= n;i++)if(!Pre[i]) DFS (i); the } the  the BOOLTopsort (intN) { thequeue<int>s; -      for(inti =1; I <= N; i++) { in         if(!inch[i]) s.push (i); the         if(s.size () = =2)return false; the     } About      while(!S.empty ()) { the         intU =S.front (); S.pop (); the         BOOLFlag =false; the          for(inti =0; I < g[u].size (); i++) { +             intv =G[u][i]; -             inch[V]-=1; the             if(!inch[v]) {Bayi                 if(flag)return false; the S.push (v); theFlag =true; -             } -         } the     } the     return true; the } the  -  the intMain () { the     intT; thescanf"%d",&T);94      while(t--){ thescanf"%d%d",&n,&m); the init (); the          for(inti =1; I <= m;i++){98             intu,v; Aboutscanf"%d%d",&u,&v); - addedges (u,v);101         }102 FIND_SCC ();103         if(SCNT = =1) {104Puts"Yes"); the             Continue;106         }107          for(inti =1; I <= scnt;i++) g[i].clear ();108          for(intU =1; u <= n;u++){109              for(inti = First[u];~i;i =E[i].next) { the                 intv =e[i].v;111                 if(Sc[u]! =Sc[v]) { the G[sc[u]].push_back (Sc[v]);113                     inch[sc[v]]++; the                 } the             } the         }117         if(Topsort (SCNT)) puts ("Yes");118         ElsePuts"No");119     } -     return 0;121}

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POJ 2762 going from U-V or from V to u? "Strong Connectivity topology sequencing"