poj 1637 Sightseeing tour 混合图欧拉回路模板（不考虑不连通的情况）

#include <cstdio>
#include <algorithm>
#include <queue>
#include <cstring>
using namespace std;
typedef int lint;
const int maxn = 10005;
const int maxm = 20005;
const lint inf = 0x3f3f3f3f;
struct dinic{
    static const int N = 10005;
    static const int M = 500005;
    static const lint inf = 0x3f3f3f3f;
    int he[N],ne[M],ver[M],d[N];
    lint edge[M];
    int s,t,tot;
    queue<int> que;
    void init( int n ){
        for( int i = 0;i <= n;i++ ){
            he[i] = 0;
        }
        tot = 1;
    }
    void add( int x,int y,lint z ){
        ver[++tot] = y; ne[ tot ] = he[x]; he[x] = tot; edge[ tot ] = z;
        ver[++tot] = x; ne[tot] = he[y]; he[y] = tot;edge[tot] = 0;
    }
    bool bfs(){
        memset( d,0,sizeof( d ) );
        while( que.size() ) que.pop();
        que.push( s );
        d[s] = 1;
        while( que.size() ){
            int x = que.front();
            que.pop();
            for( int cure = he[x];cure;cure = ne[cure] ){
                int y = ver[cure];
                if( edge[cure] && !d[y] ){
                    que.push( y );
                    d[ y ] = d[x] + 1;
                    if( y == t ) return 1;
                }
            }
        }
        return 0;
    }
    lint dfs( int x,lint flow ){
        if( x== t ) return flow;
        lint rest = flow,k;
        for( int cure = he[x];cure && rest;cure = ne[cure] ){
            int y = ver[cure];
            if( edge[cure] && d[ y ] == d[x] + 1 ){
                k = dfs( y,min( rest,edge[cure] ) );
                if( !k ) d[ y ] = 0;
                edge[cure] -= k;
                edge[ cure^1 ] += k;
                rest -= k;
            }
        }
        return flow - rest;
    }
    lint max_flow( int x,int y ){
        s = x; t = y;
        lint maxflow = 0;
        lint flow = 0;
        while( bfs() )
            while( flow = dfs( s,inf ) ) maxflow += flow;
        return maxflow;
    }
}  g;
int du[maxn],u[maxm],v[maxm],d[maxm],tot,S,T;
bool build( int m,int n ){
    tot = 0;
    g.init(T);
    for( int i = 1;i <= n;i++ ){
        du[i] = 0;
    }
    for (int i = 1; i <= m; i++) {
        scanf("%d%d%d", &u[i], &v[i], &d[i]);
    }
    for( int i = 1;i <= m;i++ ){
        du[ u[i] ]--;du[ v[i] ]++;
        if( d[i] != 1 ){
            g.add( v[i],u[i],1 );
        }
    }
    for( int i = 1;i <= n;i++ ){
        if( du[i]&1 ) return false;
        if( du[i] > 0 ){
            tot += du[i] / 2;
            g.add( S,i,du[i]/2 );
        }else if( du[i] < 0 ){
            g.add( i,T,-du[i]/2 );
        }
    }
    return true;
}
int main(){
    int ca;
    scanf("%d",&ca);
    while( ca-- ) {
        bool flag = true;
        int n, m;
        scanf("%d%d", &n, &m);
        S = n+2, T = n + 1;
        if(flag) {
            flag = build(m, n);
            if(!flag){
                puts("impossible");
                continue;
            }
            int res = g.max_flow(S, T);
            if (res== tot) {
                flag = true;
            } else flag = false;
        }
        if( flag ) puts("possible");
        else puts( "impossible" );
    }
    return 0;
}