【关节点+桥】关节点和桥模板 Tarjan

#include <cstdio>#include <cstring>#include <algorithm>using namespace std;const int N = 1e5, M = 1e5;struct Edge {    int v, next, idx;    Edge(){}    Edge(int _v, int _next, int _idx):        v(_v), next(_next), idx(_idx){}}e[M];int dfn[N], deep, head[N], tot;bool iscut[N], isbri[M];void __init__(){    tot = deep = 0;    memset(head, -1, sizeof(head));    memset(dfn, 0, sizeof(dfn));    memset(iscut, 0, sizeof(iscut));    memset(isbri, 0, sizeof(isbri));}void add(int u, int v, int idx){    e[tot] = Edge(v, head[u], idx);    head[u] = tot++;}//lowi:i及其子孙通过回边所能走到的最早的祖先的dfn值int dfs(int u, int fa){    int lowu = dfn[u] = ++deep;//打上时间戳，并初始化low值    int son = 0;//儿子数为0    for(int i = head[u]; ~i; i = e[i].next) {        int v = e[i].v;        if(!dfn[v]) {//下一个点指向儿子            son++;            int lowv = dfs(v, u);            lowu = min(lowu, lowv);            if(lowv >= dfn[u]) iscut[u] = 1;//没有回边，是关节点            if(lowv > dfn[u]) isbri[e[i].idx] = true;        }        else if(dfn[v] < dfn[u] && v != fa)//指向爷爷，发现回边            lowu = min(lowu, dfn[v]);//利用回边来更新low值    }    if(fa == -1 && son == 1) iscut[u] = 0;//只有1个儿子的根结点不是割顶    return lowu;}int main(){    __init__();    return 0;}