poj 1637 Sightseeing tour 混和欧拉图 dinic

#pragma comment(linker, "/STACK:102400000,102400000")
#include<stdio.h>
#include<string.h>
#include<queue>
#include<vector>
using namespace std;
const int N=1024;
const int inf=1<<24;

struct Edge
{
int from,to,cap,flow;
};
vector<Edge>edges;
vector<int>G
;
int n,m,s,t;
int vis
;
int d
;
int cur
;

void AddEdge(int from,int to,int cap)
{
Edge tp;
tp.from=from,tp.to=to,tp.cap=cap,tp.flow=0;
edges.push_back(tp);

tp.from=to,tp.to=from,tp.cap=0,tp.flow=0;
edges.push_back(tp);

int g_size=edges.size();
G[from].push_back(g_size-2);
G[to].push_back(g_size-1);
}

bool BFS()
{
memset(vis,0,sizeof(vis));
queue<int>Q;
Q.push(s);
d[s]=0;
vis[s]=1;
while(!Q.empty())
{
int x=Q.front();
Q.pop();
for(int i=0; i<G[x].size(); i++)
{
Edge &e=edges[G[x][i]];
if(!vis[e.to]&&e.cap>e.flow)
{
vis[e.to]=1;
d[e.to]=d[x]+1;
Q.push(e.to);
}
}
}
return vis[t];
}

int DFS(int x,int a)
{
if(x==t||a==0) return a;
int flow=0,f;
for(int &i=cur[x]; i<G[x].size(); i++)
{
Edge &e=edges[G[x][i]];
if(d[x]+1==d[e.to]&&(f=DFS(e.to,min(a,e.cap-e.flow)))>0)
{
e.flow+=f;
edges[G[x][i]^1].flow-=f;
flow+=f;
a-=f;
if(a==0) break;
}
}
return flow;
}

int Maxflow(int st,int ed)
{
int flow=0;
while(BFS())
{
memset(cur,0,sizeof(cur));
flow+=DFS(st,inf);
}
return flow;
}

int main()
{

int i,j,_,u,v,c,flow,f,mp

,in
,out
;
scanf("%d",&_);
while(_--)
{
scanf("%d%d",&n,&s);
memset(mp,0,sizeof(mp));
memset(in,0,sizeof(in));
memset(out,0,sizeof(out));
edges.clear();
for(i=0;i<N;i++) G[i].clear();
for(i=0;i<s;i++)
{
scanf("%d%d%d",&u,&v,&c);
if(c==0) mp[u][v]++;
out[u]++;
in[v]++;
}
f=1;
s=0;
t=n+1;
for(i=1,flow=0;i<=n;i++)
{
int tp=in[i]-out[i];
if(tp>0) flow+=tp/2;
else tp=-tp;
if(tp%2==1) {f=0;break;}

}
if(f==0) {printf("impossible\n");continue;}
for(i=1;i<=n;i++)
{
if(in[i]>out[i])
AddEdge(s,i,(in[i]-out[i])/2);
else
AddEdge(i,t,(out[i]-in[i])/2);
for(j=1;j<=n;j++)
if(mp[i][j])
AddEdge(j,i,mp[i][j]);
}
if(Maxflow(s,t)==flow)
printf("possible\n");
else
printf("impossible\n");
}
return 0;
}