POJ1637, maximum flow is determined whether there is mixed FIG Euler

Topic Link: Sightseeing Tour
this article put it very well: Mixed Graphs Euler method for solving general said
my code:

/*************************************************************************
	> File Name: main.cpp
	> Author:Eagles 
	> Mail:None 
	> Created Time: 2018年09月29日 星期六 20时05分28秒
	> Description:POJ1637 
 ************************************************************************/

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
#include<vector>
#include<stack>
#include<bitset>
#include<cstdlib>
#include<set>
#include<list>
#include<deque>
#include<map>
#include<queue>
using namespace std;
#define N 10000
struct node
{
    int to;
    int nex;
    int val;
}E[N*N];
int head[N];
int lev[N];
int ind[N],outd[N];
int n,m,cnt;
int flow;
int S,T;
void addEdge(int a, int b, int val)
{

    E[cnt].to=b;
    E[cnt].val=val;
    E[cnt].nex=head[a];
    head[a]=cnt++;

    E[cnt].to=a;
    E[cnt].val=0;
    E[cnt].nex=head[b];
    head[b]=cnt++;

}

void init()
{
    memset(head,-1,sizeof(head));
    memset(ind,0,sizeof(ind));
    memset(outd,0,sizeof(outd));
    cnt=flow=0;

    scanf("%d%d",&n,&m);
    S=0,T=n+1;
    while (m--)
    {
        int a,b,c;
        scanf("%d%d%d",&a,&b,&c);
        outd[a]++;
        ind[b]++;

        if (a != b)
        {
            if (!c)
                addEdge(a,b,1);
        }
    }
}

bool build()
{
    for (int i=1; i<=n; i++)
    {
        if ((ind[i]+outd[i])&1)
            return false;
        if (outd[i] > ind[i])
        {
            int d=abs(ind[i]-outd[i]);
            int x=d/2;
            flow+=x;
            addEdge(S,i,x);
        }
        else if (outd[i] < ind[i])
        {
            int d=abs(outd[i]-ind[i]);
            int x=d/2;

            addEdge(i,T,x);
        }
    }

    return true;
}

bool bfs()
{
    queue<int>q;
    memset(lev,0,sizeof(lev));
    q.push(S);
    lev[S]=1;

    while (!q.empty())
    {
        int u=q.front();
        q.pop();

        for (int i=head[u]; i!=-1; i=E[i].nex)
        {
            int v=E[i].to;

            if (E[i].val > 0 &&lev[v]==0)
            {
                lev[v]=lev[u]+1;
                q.push(v);

                if (v == T)
                    return true;
            }
        }
    }
    return false;
}

int dfs(int u, int f)
{
    if (u == T)
        return f;
    int tag=0;

    for (int i=head[u]; i!=-1; i=E[i].nex)
    {
        int v=E[i].to;

        if (E[i].val >0 &&lev[v]==lev[u]+1)
        {
            int d=dfs(v,min(f-tag,E[i].val));
            E[i].val-=d;
            E[i^1].val+=d;
            tag+=d;

            if (tag == f)
                return f;
        }
    }
    return tag;
}

int Dinic()
{
    int ans=0;
    int inf=10000000;

    while (bfs())
    {
        ans+=dfs(S,inf);
    }

    return ans;
}

int main()
{
    int t;
    scanf("%d",&t);
    while (t--)
    {
        init();
        if (!build())
        {
            printf("impossible\n");
            continue;
        }
        int ans=Dinic();
        if (ans == flow)
            printf("possible\n");
        else
            printf("impossible\n");
    }
    return 0;
}