网络流求卡常

bool bfs(){
    for(ll i=0;i<=n+1;i++) d[i]=-1,g[i]=h[i];
    ll H=1,T=1; q[1]=n,d[n]=0;
    while(H<=T){
        for(ll i=h[q[H]];i;i=x[i]){
            if(!w[i]||d[k[i]]>=0) continue;
            d[k[i]]=d[q[H]]+1,q[++T]=k[i];
            if(k[i]>n) return 1;
        }
        H++;
    }
    return 0;
}
ll dfs(ll u,ll l){
    if(u>n) return l; ll f=0;
    for(ll i=g[u];i&&l;i=x[i]){
        g[u]=i;
        if(d[u]+1!=d[k[i]]) continue;
        ll t=dfs(k[i],min(l-f,w[i]));
        f+=t,w[i]-=t,w[i^1]+=t;
    }
    return f;
}