POJ 2762 Tarjan + set + degrees

Source: Internet
Author: User

Going from U-V or from V to u?
Time Limit: 2000MS Memory Limit: 65536K
Total Submissions: 15494 Accepted: 4100

Description

In order to make their sons brave, Jiajia and wind take them to a big cave. The cave has n rooms, and one-way corridors connecting some rooms. Each time, wind choose the rooms x and Y, and ask one of the their little sons go from one to the other. The son can either go from X-to-y, or from Y to X. Wind promised that her tasks is all possible, but she actually doesn ' t Know how to decide if a task is possible. To make hers life easier, Jiajia decided to choose a cave in which every pair of rooms are a possible task. Given a cave, can you tell Jiajia whether wind can randomly choose both rooms without worrying about anything?

Input

The first line contains a single integer T, the number of test cases. and followed T cases.

The first line is contains integers n, m (0 < N < 1001,m < 6000), the number of rooms and corridors In the cave. The next m lines each contains to integers u and V, indicating that there is a corridor connecting the class U and the Class V dire ctly.

Output

The output should contain T lines. Write ' Yes ' if the cave have the property stated above, or ' No ' otherwise.

Sample Input

13 31 22) 33 1

Sample Output

Yes

Source

POJ Monthly--2006.02.26,zgl & twb topic meaning: To give a direction graph of n points, M-bars, ask whether it is arbitrary to select two points U and V, whether it can reach V from U or reach u from v. Ideas:
If there are multiple weakly connected components, then it is definitely not reachable, so use and check the set processing. The interior of the strong connected component is arbitrarily two points are reached each other, do not reach each other points between the strong connected components, so first with Tarjan strong connectivity components, if the number of degrees of 0 >=2| | The number of >=2 is 0, so it is not reachable. Various conditions can be judged. Code:
1#include <cstdio>2#include <cstring>3#include <algorithm>4#include <iostream>5#include <vector>6#include <queue>7#include <cmath>8#include <Set>9#include <stack>Ten using namespacestd; One  A #defineN 1005 -  - intMaxintXintY) {returnX>y?x:y;} the intMinintXintY) {returnX<y?x:y;} - intAbsintXintY) {returnx<0?-x:x;} -  - intN, M; + BOOL inch[N]; - intSuo[n]; + intCNT; Avector<int>Ve[n]; at intDfn[n], low[n], time; -stack<int>St; - intFather[n]; -  - intFindrootintu) { -     if(father[u]!=u) father[u]=Findroot (Father[u]); in     returnFather[u]; - } to  + voidTarjan (intu) { -dfn[u]=low[u]=time++; theSt.push (U);inch[u]=true; *     intI, J, K; $      for(i=0; I<ve[u].size (); i++){Panax Notoginseng         intv=Ve[u][i]; -         if(dfn[v]==-1){ the Tarjan (v); +low[u]=min (low[u],low[v]); A         } the         Else if(inch[v]) low[u]=min (low[u],dfn[v]); +     } -     if(dfn[u]==Low[u]) { $          while(1){ $             intx=st.top (); -suo[x]=CNT; -             inch[x]=false; the St.pop (); -             if(x==u| | St.empty ()) Break;Wuyi         } thecnt++; -     } Wu } -  About Main () $ { -     intI, J, K, U, v; -     intT; -Cin>>T; A      +      while(t--){ thescanf"%d%d",&n,&m); -          for(i=0; i<=n;i++) ve[i].clear (); $          for(i=0; i<m;i++){ thescanf"%d%d",&u,&v); the Ve[u].push_back (v); the         } theTime=cnt=1; -memset (dfn,-1,sizeof(DFN)); in          while(!st.empty ()) St.pop (); theMemsetinch,false,sizeof(inch)); the          for(i=1; i<=n;i++){ About             if(dfn[i]==-1){ the Tarjan (i); the             } the         } +         intInn[n], out[N]; -memset (INN,0,sizeof(INN)); theMemset out,0,sizeof( out));Bayi          for(i=1; i<=n;i++) father[i]=i; the          for(i=1; i<=n;i++){ the              for(j=0; J<ve[i].size (); j + +){ -                 intU=suo[i], v=Suo[ve[i][j]]; -                 if(u!=v) { theFather[findroot (v)]=findroot (u); theinn[v]++; the                      out[u]++; the                 } -             } the         } the          the         intnum=0;94          for(i=1; i<cnt;i++){ the             if(father[i]==i) num++; the         } the         if(num>1) {98printf"no\n");Continue; About         } -     101         intN1, N2;102N1=n2=0;103          for(i=1; i<cnt;i++){104             if(!inn[i]) n1++; the             if(! out[i]) n2++;106         }107         if(n1>1|| N2>1) printf ("no\n");108         Elseprintf"yes\n");109     } the}

POJ 2762 Tarjan + set + degrees

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.