1 #include<iostream>
2 #include<algorithm>
3 #include<cstring>
4 #include<vector>
5 #include<set>
6 #include<map>
7 #include<queue>
8 using namespace std;
9 #define INF 0x3f3f3f3f
10 #define M(a, b) memset(a, b, sizeof(a))
11 const int N = 1e4 + 10, M = 20;
12 int deep[N], p[N][25];
13 vector<int> G[N];
14
15 void dfs(int u, int fa) {
16 for (int i = 1; i <= M; ++i)
17 p[u][i] = p[p[u][i-1]][i-1];
18 for (int i = 0; i < G[u].size(); ++i) {
19 int v = G[u][i];
20 if (v == fa || deep[v]) continue;
21 deep[v] = deep[u] + 1;
22 p[v][0] = u;
23 dfs(v, u);
24 }
25 }
26
27 int lca(int a, int b) {
28 if (deep[a] < deep[b]) swap(a, b);
29 for (int det = deep[a]-deep[b], i = 0; det; det >>= 1, ++i)
30 if (det & 1) a = p[a][i];
31 if (a == b) return a;
32 for (int i = M-1; i >= 0; --i) {
33 if (p[a][i] == p[b][i]) continue;
34 a = p[a][i];
35 b = p[b][i];
36 }
37 return p[a][0];
38 }
