【混合图欧拉路判定】【poj 1637】Sightseeing tour

//#define _TEST _TEST
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <iostream>
#include <cmath>
#include <algorithm>
using namespace std;
/************************************************
Code By willinglive    Blog:http://willinglive.cf
************************************************/
#define rep(i,l,r) for(int i=(l),___t=(r);i<=___t;i++)
#define per(i,r,l) for(int i=(r),___t=(l);i>=___t;i--)
#define MS(arr,x) memset(arr,x,sizeof(arr))
#define LL long long
#define INE(i,u,e) for(int i=head[u];~i;i=e[i].next)
inline const int read()
{int r=0,k=1;char c=getchar();for(;c<'0'||c>'9';c=getchar())if(c=='-')k=-1;
for(;c>='0'&&c<='9';c=getchar())r=r*10+c-'0';return k*r;}
/////////////////////////////////////////////////
const int inf=0x3f3f3f3f;
int n,m;
struct edge{int v,flow,cap,next;}e[2222];
int head[222],k;
int ind[222],outd[222];

int S,T;
int cur[222],d[222],q[222];
/////////////////////////////////////////////////
void adde(int u,int v,int f){e[k].v=v;e[k].flow=0;e[k].cap=f;e[k].next=head[u];head[u]=k++;}
void ins(int u,int v,int f1,int f2){adde(u,v,f1);adde(v,u,f2);}
inline int F(int i){return e[i].cap-e[i].flow;}
bool bfs()
{
MS(d,-1); d[q[0]=S]=0; memcpy(cur,head,sizeof(cur));
for(int u,v,l=0,r=1;l<r;)
{
u=q[l++];
INE(i,u,e) if(F(i)&&d[v=e[i].v]==-1)
{
q[r++]=v; d[v]=d[u]+1;
if(v==T) return 1;
}
}
return 0;
}
int dfs(int u,int a)
{
if(u==T||a==0) return a;
for(int &i=cur[u];~i;i=e[i].next) if(F(i)&&d[e[i].v]==d[u]+1)
{
if(int t=dfs(e[i].v,min(a,F(i))))
{
e[i].flow+=t; e[i^1].flow-=t;
return t;
}
}
return 0;
}
int dinic()
{
int f=0;
while(bfs()) while(int t=dfs(S,inf)) f+=t;
return f;
}
/////////////////////////////////////////////////
void input()
{
MS(head,-1); k=0; MS(ind,0); MS(outd,0);

scanf("%d%d",&n,&m);
int u,v,w;
rep(i,1,m)
{
scanf("%d%d%d",&u,&v,&w);
ind[v]++; outd[u]++;
if(w==0) ins(u,v,1,0);
}
}
void solve()
{
S=0; T=n+1;
rep(i,1,n)
{
if((ind[i]-outd[i])&1){puts("impossible");return;}
}
int sum=0;
rep(i,1,n)
{
if(ind[i]<outd[i])
{
ins(S,i,(outd[i]-ind[i])>>1,0);
}
else if(ind[i]>outd[i])
{
ins(i,T,(ind[i]-outd[i])>>1,0);
sum+=(ind[i]-outd[i])>>1;
}
}
if(sum==dinic()) puts("possible");
else puts("impossible");
}
/////////////////////////////////////////////////
int main()
{
#ifndef _TEST
freopen("std.in","r",stdin); freopen("std.out","w",stdout);
#endif
rep(i,1,read())
input(),solve();
return 0;
}