1 Source Code
 2 Problem: 1637        User: sdfzyhy
 3 Memory: 1148K        Time: 32MS
 4 Language: G++        Result: Accepted
 5 
 6     Source Code
 7 
 8     //BZOJ 1000
 9     #include<vector>
10     #include<cstdio>
11     #include<cstdlib>
12     #include<cstring>
13     #include<iostream>
14     #include<algorithm>
15     #define rep(i,n) for(int i=0;i<n;++i)
16     #define F(i,j,n) for(int i=j;i<=n;++i)
17     #define D(i,j,n) for(int i=j;i>=n;--i)
18     using namespace std;
19 
20     int getint(){
21         int v=0,sign=1; char ch=getchar();
22         while(ch<‘0‘||ch>‘9‘) {if (ch==‘-‘) sign=-1; ch=getchar();}
23         while(ch>=‘0‘&&ch<=‘9‘) {v=v*10+ch-‘0‘; ch=getchar();}
24         return v*sign;
25     }
26     typedef long long LL;
27     const int N=100010,M=100010,INF=~0u>>2;
28     /*******************tamplate********************/
29     int n,m,ans,du[1000];
30     struct edge{int to,v;};
31     struct Net{
32         edge E[M];
33         int next[M],head[N],cnt;
34         void ins(int x,int y,int z){E[++cnt]=(edge){y,z};next[cnt]=head[x];head[x]=cnt;}
35         void add(int x,int y,int z){ins(x,y,z); ins(y,x,0);}
36         int S,T,d[N],Q[M],cur[N];
37         bool mklevel(){
38             F(i,0,T) d[i]=-1;
39             int l=0,r=-1;
40             Q[++r]=S; d[S]=0;
41             while(l<=r){
42                 int x=Q[l++];
43                 for(int i=head[x];i;i=next[i])
44                     if(E[i].v && d[E[i].to]==-1){
45                         d[E[i].to]=d[x]+1;
46                         Q[++r]=E[i].to;
47                     }
48             }
49             return d[T]!=-1;
50         }
51         int dfs(int x,int a){
52             if(x==T)return a;
53             int flow=0;
54             for(int &i=cur[x];i && flow<a;i=next[i])
55                 if(E[i].v && d[E[i].to]==d[x]+1){
56                     int f=dfs(E[i].to,min(a-flow,E[i].v));
57                     E[i].v-=f;
58                     E[i^1].v+=f;
59                     flow+=f;
60                 }
61             if(!flow) d[x]=-1;
62             return flow;
63         }
64         void Dinic(){
65             while(mklevel()){
66                 F(i,S,T) cur[i]=head[i];
67                 ans+=dfs(S,INF);
68             }
69         }
70         void init(){
71             n=getint(); m=getint();
72             cnt=1; memset(head,0,sizeof head);
73             F(i,1,n) du[i]=0;
74             S=0; T=n+m+2; ans=0;
75             int x,y,z;
76             F(i,1,m){
77                 x=getint(); y=getint(); z=getint();
78                 add(S,i,1); add(i,y+m,1);
79                 if (!z) add(i,x+m,1);
80                 du[x]++; du[y]++;
81             }
82             F(i,1,n){
83                 if (du[i]%2){puts("impossible");return;}
84                 add(i+m,T,du[i]/2);
85             }
86             Dinic();
87             if (ans==m) puts("possible");
88             else puts("impossible");
89         }
90     }G1;
91     int main(){
92     #ifndef ONLINE_JUDGE
93         freopen("input.txt","r",stdin);
94     //    freopen("output.txt","w",stdout);
95     #endif
96         int T=getint();
97         while(T--) G1.init();
98         return 0;
99     }