割边的tarjan算法

bool vis[maxn];
int dfn[maxn],low[maxn];
int cnt;
vector<int>gra[maxn];
void cutPoint(int u,int v){
    vis[u]=true;
    dfn[u]=low[u]=++cnt;
    int child=0;
    int sz=gra[u].size();
    for(int i=0;i<sz;i++){
        int v=gra[u][i];
        if(v!=f&&vis[v]){
            low[u]=min(low[u],dfn[v]);
        }else if(!vis[v]){
            child++;
            cutPoint(u,v);
            low[u]=min(low[u],low[v]);
            if(f!=-1&&low[v]>dfn[u]){
                printf("%d-%d\n",u,v);
            }
        }
    }
}