【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;//仅仅有1个儿子的根结点不是割顶
    return lowu;
}

int main()
{
    __init__();
    return 0;
}