@[yyrwlj](/user/965685)
改成这样，原因是必须让重链上 dfn 连续。
```cpp
void dfs2(int u, int fa, int Top) {
top[u] = Top;
dfn[u] = ++vis_cnt;
if (big_son[u])
dfs2(big_son[u], u, Top);
for (int i = h[u]; i; i = g[i].nxt) {
int j = g[i].to;
if (j == big_son[u])
num[dfn[j]] = g[i].e;
if (j == fa || j == big_son[u])
continue;
dfs2(j, u, j);
num[dfn[j]] = g[i].e;
}
}
```
by Usada_Pekora @ 2023-12-28 19:10:52
@[Usada_Pekora](/user/434929) 这把眼瞎局 /bx
by yyrwlj @ 2023-12-28 19:17:17