POJ1094 alphabetical order (topological sort)

The question test instructions clear, that is, given a set of letters of the size of the relationship to determine whether they can form a unique topological sequence. is a typical topological sort, but there are three types of output formats:

1. The letter sequence is ordered and output sequentially;

2. The sequence does not determine whether it is orderly;

3. There is a contradiction between the sequence alphabetical order, that is, a ring exists.

And these three forms of judgment are in order: first to determine whether there is a ring (3), and then determine whether the order (1), finally can determine whether the results (2). Note: for (2) the entire graph must be traversed, and (1) and (3) Once the result is reached, the subsequent input is not processed.

1#include <iostream>2#include <cstdio>3#include <cstring>4#include <vector>5#include <algorithm>6 7 using namespacestd;8 9 Const intn=5005;Tenvector<int>G[n]; One intDfn[n],low[n],dg[n],tim; A BOOLVis[n],map[n][n]; - intN,r; -  the voidTarjan (intUintFA) - { -dfn[u]=low[u]=++Tim; -vis[u]=1; +      for(intI=0; I<g[u].size (); i++) -     { +         intv=G[u][i]; A         if(V==FA)Continue; at         if(!Dfn[v]) -         { - Tarjan (V, u); -low[u]=min (low[u],low[v]); -         } -         Else if(Vis[v]) low[u]=min (low[u],dfn[v]); in     } - } to voidInit () + { -memset (DFN,0,sizeof(DFN));  thememset (Low,0,sizeof(low));  *memset (Vis,0,sizeof(VIS));  $tim=0;Panax NotoginsengTarjan (1,-1); - } the intMain () + { A      while(~SCANF ("%d%d",&n,&R)) the     { +          for(intI=1; i<=n;i++)  - g[i].clear (); $memset (Map,0,sizeof(map)); $         intu,v; -          for(intI=0; i<r;i++) -         { thescanf"%d%d",&u,&v);  -             if(!Map[u][v])Wuyi             { the G[u].push_back (v); - g[v].push_back (u); Wumap[u][v]=map[v][u]=1; -             } About         } $  - init (); -memset (DG,0,sizeof(DG)); -          A          for(intu=1; u<=n;u++) +              for(intI=0; I<g[u].size (); i++) the             { -                 intv=G[u][i]; $                 if(Low[u]!=low[v]) dg[low[u]]++;  the             } the  the         intCnt=0; the          for(intI=1; i<=n;i++) -             if(dg[i]==1) cnt++; inprintf"%d\n", (cnt+1)/2); the     } the}

POJ1094 alphabetical order (topological sort)