poj 1637 Sightseeing tour 混合欧拉 最大流

#include <cstdio>
#include <vector>
#include <queue>
#include <cstring>
using namespace std;
#define maxn 230
#define INF 100000
struct Edge
{
	int from, to, cap, flow;
};

int n, m, s, t;
vector<Edge> edges;    // 边数的两倍
vector<int> G[maxn];   // 邻接表，G[i][j]表示结点i的第j条边在e数组中的序号
bool vis[maxn];        // BFS使用
int d[maxn];           // 从起点到i的距离
int cur[maxn];         // 当前弧指针
int in[maxn],out[maxn];
int min(int a,int b)
{
	if(a<b) return a;
	else return b;
}
void AddEdge(int from, int to, int cap)
{
	int len;
	Edge temp;
	temp.from=from;temp.to=to;temp.cap=cap;temp.flow=0;
	edges.push_back(temp);
	temp.from=to;temp.to=from;temp.cap=0;temp.flow=0;
    edges.push_back(temp);
    len = edges.size();
    G[from].push_back(len-2);
    G[to].push_back(len-1);
}
bool BFS()
{
	memset(vis, 0, sizeof(vis));
    queue<int> Q;
    Q.push(s);
    vis[s] = 1;
    d[s] = 0;
    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 flow = 0;
    while(BFS())
	{
		memset(cur, 0, sizeof(cur));
		flow += DFS(s, INF);
    }
    return flow;
}
int main()
{
    int cas;
    int i;
    int x,y,z;
    scanf("%d",&cas);
    while(cas--)
    {
        scanf("%d%d",&n,&m);
        for(i=0;i<=n+10;i++) G[i].clear();
        memset(in,0,sizeof(in));
        memset(out,0,sizeof(out));
        s=0;t=n+1;
        for(i=1;i<=m;i++)
        {
            scanf("%d%d%d",&x,&y,&z);
            if(z==1)
            {
                out[x]++;
                in[y]++;
            }
            else
            {
                out[x]++;
                in[y]++;
                AddEdge(x,y,1);
            }
        }
        int sum=0;
        int flag=1;
        for(i=1;i<=n;i++)
        {
            int ans=in[i]-out[i];
            if(ans<0) ans=-ans;
            if(ans%2==1)
            {
                flag=0;
                break;
            }
            if((in[i]-out[i])>0)
                AddEdge(i,t,(in[i]-out[i])/2);
            else if((in[i]-out[i])<0)
            {
                AddEdge(s,i,(out[i]-in[i])/2);
                sum=sum+(out[i]-in[i])/2;
            }
        }
        if(Maxflow()==sum&&flag==1)
            printf("possible\n");
        else printf("impossible\n");
    }
    return 0;
}