求无向图中的割边(桥)

inline void tarjan(int x,int edge) {
    int v;
    dfn[x] = low[x] = ++tot;
    for(int i = head[x];i != -1; i = e[i].next) {
        v = e[i].to;
        if(!dfn[v]) {
            tarjan(v,i);
            low[x] = min(low[x],low[v]);
            if(low[v] > dfn[x])
                bridge[i] = bridge[i^1] = true;
        }
        else if(i != edge)
                low[x] = min(low[x],dfn[v]);
    }
}