POJ 1637 Sightseeing tour(混合图的欧拉回路）

#include <cstdio>
#include <cstring>
#include <iostream>
#include <map>
#include <algorithm>
#include <vector>
#include <string>
#include <queue>
using namespace std;
#define INF 0x3ffffff
struct node
{
    int u,v,next,re,w;
}edge[20001];
int first[2001],dis[2001];
int in[2001],out[2001];
int t,str,end;
void CL()
{
    t = 1;
    memset(first,-1,sizeof(first));
}
void add(int u,int v,int w)
{
    edge[t].u = u;
    edge[t].v = v;
    edge[t].w = w;
    edge[t].re = t + 1;
    edge[t].next = first[u];
    first[u] = t ++;
    edge[t].u = v;
    edge[t].v = u;
    edge[t].w = 0;
    edge[t].re = t - 1;
    edge[t].next = first[v];
    first[v] = t ++;
}
int bfs()
{
    int u,v,i;
    memset(dis,-1,sizeof(dis));
    queue<int> que;
    que.push(str);
    dis[str] = 0;
    while(!que.empty())
    {
        u = que.front();
        que.pop();
        for(i = first[u];i != -1;i = edge[i].next)
        {
            v = edge[i].v;
            if(edge[i].w > 0&&dis[v] < 0)
            {
                dis[v] = dis[u] + 1;
                que.push(v);
            }
        }
    }
    if(dis[end] > 0) return 1;
    else return 0;
}
int dfs(int u,int step)
{
    int i,temp,v,tf = 0;
    if(u == end) return step;
    for(i = first[u];i != -1;i = edge[i].next)
    {
        v = edge[i].v;
        if(edge[i].w > 0&&dis[v] == dis[u] + 1&&(temp = dfs(v,min(step,edge[i].w))))
        {
            edge[i].w -= temp;
            edge[edge[i].re].w += temp;
            return temp;
        }
    }
    if(!tf) dis[u] = -1;
    return tf;
}
int main()
{
    int t,i,u,v,k,n,m;
    scanf("%d",&t);
    while(t--)
    {
        memset(in,0,sizeof(in));
        memset(out,0,sizeof(out));
        scanf("%d%d",&n,&m);
        CL();
        str = 0;
        end = n + 1;
        for(i = 0;i < m;i ++)
        {
            scanf("%d%d%d",&u,&v,&k);
            in[u] ++;
            out[v] ++;
            if(k != 1)
            add(u,v,1);
        }
        for(i = 1;i <= n;i ++)
        {
            if(abs(in[i]-out[i])%2 == 1)
            break;
        }
        if(i != n+1)
        {
            printf("impossible\n");
            continue;
        }
        int sum = 0;
        for(i = 1;i <= n;i ++)
        {
            if(in[i] > out[i])
            {
                add(str,i,(in[i]-out[i])/2);
                sum += (in[i]-out[i])/2;
            }
            else
            {
                add(i,end,(out[i]-in[i])/2);
            }
        }
        int ans = 0,res;
        while(bfs())
        {
            while(res = dfs(str,INF))
            ans += res;
        }
        if(ans == sum)
        printf("possible\n");
        else
        printf("impossible\n");
    }
    return 0;
}