std::vector<int> tree[maxn]; int fa[maxn]; void dfs(int u,int father) { int len = tree[u].size(); for (int i = 0;i < len;i++) { int v = tree[u][i]; if (v != father) dfs(v,fa[v] = u); } }
无根树转有根树
原文：https://www.cnblogs.com/-Ackerman/p/12228381.html
