poj 2762 Going from u to v or from v to u?

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <ctype.h>
#include <math.h>
#include <time.h>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <vector>
#include <string>
#include <iostream>
#include <algorithm>
using namespace std;

#define ull unsigned __int64
//#define ll __int64
//#define ull unsigned long long
#define ll long long
#define son1 New(p.xl,xm,p.yl,ym),(rt<<2)-2
#define son2 New(p.xl,xm,min(ym+1,p.yr),p.yr),(rt<<2)-1
#define son3 New(min(xm+1,p.xr),p.xr,p.yl,ym),rt<<2
#define son4 New(min(xm+1,p.xr),p.xr,min(ym+1,p.yr),p.yr),rt<<2|1
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define middle (l+r)>>1
#define MOD 1000000007
#define esp (1e-8)
const int INF=0x3F3F3F3F;
const double DINF=10000.00;
//const double pi=acos(-1.0);
const int M=6010;
int min(int x,int y){return x<y? x:y;}
int max(int x,int y){return x>y? x:y;}
void swap(int& x,int& y){int t=x;x=y;y=t;}
int T,cas;

struct node{int v,next;}edge[M<<1];
int init[M];
int n,m,len;
int In[M];

bool judge(){
int u,v,i,tot=0,cnt;
while(tot<=n){
cnt=0;
for(i=1;i<=n;i++) if(!In[i]) u=i,cnt++;
if(!cnt) return true;
if(cnt>1) return false;
for(i=init[u];i!=-1;i=edge[i].next) v=edge[i].v,In[v]--;
In[u]=-1;
tot++;
}
return true;
}

void _init(){
scanf("%d%d",&n,&m);
memset(init,-1,sizeof(int)*(n+1));
memset(In,0,sizeof(int)*(n+1));
int u;
for(len=1;len<=m;len++){
scanf("%d%d",&u,&edge[len].v);
edge[len].next=init[u],init[u]=len;
In[edge[len].v]++;
}
}

void _sof(){
printf("%s\n",judge()? "Yes":"No");
}

int main(){
//freopen("1.in","r",stdin);
//freopen("1.out","w",stdout);
//_init(),_sof();
scanf("%d",&T);for(cas=1;cas<=T;cas++) _init(),_sof();
//while(~scanf("%d",&k)){for(int i=0;i<k;i++) _init(),_sof();}
return 0;
}