POJ 2762 going from U-V or from V to u? trajan+ topology

Going from U-V or from V to u?

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
The puzzle: to ask whether this picture is a single link; After the contraction point this figure must be a chain;
Data
3
3 2
1 2
3 2
5 4
1 2
2 3
3 4
4 5
5 4
1 2
1 3
3 4
3 5
No
Yes
No

#include <iostream>#include<cstdio>#include<cmath>#include<string>#include<queue>#include<algorithm>#include<stack>#include<cstring>#include<vector>#include<list>#include<Set>#include<map>using namespacestd;#definell __int64#defineINF 2000000001intScan () {intres =0, ch;  while( ! (ch = getchar ()) >='0'&& CH <='9' ) )    {        if(ch = = EOF)return 1<< - ; } Res= CH-'0' ;  while(ch = getchar ()) >='0'&& CH <='9') Res= Res *Ten+ (CH-'0' ) ; returnRes;}struct  is{    intu,v; intNext;} edge[50010],edgetop[50010];inthead[50010];intbelong[50010];intdfn[50010];intlow[50010];intstackk[50010];intinstack[50010];intdu[100010];intN,m,jiedge,lu,bel,top,jiedgetop;voidUpdateintUintv) {Jiedge++; EDGE[JIEDGE].U=u; EDGE[JIEDGE].V=v; Edge[jiedge].next=Head[u]; Head[u]=Jiedge;}voidUpdatetop (intUintv) {Jiedgetop++; EDGETOP[JIEDGETOP].U=u; EDGETOP[JIEDGETOP].V=v; Edgetop[jiedgetop].next=Head[u]; Head[u]=jiedgetop;}voidDfsintx) {Dfn[x]=low[x]=++Lu; stackk[++top]=x; INSTACK[X]=1;  for(intI=head[x];i;i=Edge[i].next) {        if(!DFN[EDGE[I].V])            {DFS (EDGE[I].V); LOW[X]=min (low[x],low[edge[i].v]); }        Else if(INSTACK[EDGE[I].V]) low[x]=min (low[x],dfn[edge[i].v]); }    intNE; if(low[x]==Dfn[x]) {        //cout<<x<< "" << "XXX" <<endl;bel++;  Do{NE=stackk[top--]; Belong[ne]=Bel; Instack[ne]=0; } while(x!=NE); }}voidTarjan () {memset (DFN,0,sizeof(DFN)); Bel=lu=top=0;  for(intI=1; i<=n;i++)    if(!Dfn[i]) DFS (i);}intTopsort () {intSt; intflag=0;  for(intI=1; i<=bel;i++)    {        if(du[i]==0) {flag++; St=i; }    }    if(flag>1)return 0; intn=Bel,en;  while(n--)    {        intflagg=0;  for(intI=head[st];i;i=Edgetop[i].next) {en=edgetop[i].v; Du[en]--; if(du[en]==0) {Flagg++; St=en; }        }        if(flagg>1)return 0; }    return 1;}intMain () {inti,t; intnn; scanf ("%d",&, N);  while(nn--) {scanf ("%d%d",&n,&m); memset (Head,0,sizeof(head)); Memset (Belong,0,sizeof(belong)); Jiedge=0;  for(i=1; i<=m;i++)        {            intu,v; scanf ("%d%d",&u,&v);        Update (U,V);        } Tarjan (); memset (Head,0,sizeof(head)); Memset (Du,0,sizeof(du)); Jiedgetop=0; /*cout<<bel<<endl; for (i=1;i<=n;i++) cout<<belong[i]<<endl;*/         for(intI=1; i<=m;i++)        {            intu=edge[i].u; intv=edge[i].v; if(belong[u]!=Belong[v]) {Du[belong[v]]++;            Updatetop (Belong[u],belong[v]); }        }        if(Topsort ()) printf ("yes\n"); Elseprintf ("no\n"); }    return 0;}/*3 of 2*/

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POJ 2762 going from U-V or from V to u? trajan+ topology