tarjan求LCA模板

 1 # include <iostream>
 2 # include <cstdio>
 3 # include <cstring>
 4 # include <string>
 5 # include <cmath>
 6 # include <vector>
 7 # include <map>
 8 # include <queue>
 9 # include <cstdlib>
10 # define MAXN 500001
11 using namespace std;
12 
13 inline int get_num() {
14     int k = 0, f = 1;
15     char c = getchar();
16     for(; !isdigit(c); c = getchar()) if(c == ‘-‘) f = -1;
17     for(; isdigit(c); c = getchar()) k = k * 10 + c - ‘0‘;
18     return k * f;
19 }
20 
21 int n, m, s;
22 int fa[MAXN], qx[MAXN], qy[MAXN], ans[MAXN], f[MAXN];
23 vector <int> vec[MAXN], q[MAXN];
24 
25 inline int find(int x)
26 {
27     return x == fa[x] ? x : fa[x] = find(fa[x]);
28 }
29 
30 inline void dfs(int u)
31 {
32     int i, v;
33     fa[u] = u;
34     for(i = 0; i < vec[u].size(); i++)
35     {
36         v = vec[u][i];
37         if(f[u] != v) f[v] = u, dfs(v);
38     }
39     for(i = 0; i < q[u].size(); i++)
40         if(f[v = u ^ qx[q[u][i]] ^ qy[q[u][i]]])
41             ans[q[u][i]] = find(v);
42     fa[u] = f[u];
43 }
44 
45 int main()
46 {
47     int i, x, y;
48     n = get_num();
49     m = get_num();
50     s = get_num();
51     for(i = 1; i < n; i++)
52     {
53         x = get_num();
54         y = get_num();
55         vec[x].push_back(y);
56         vec[y].push_back(x);
57     }
58     for(i = 1; i <= m; i++)
59     {
60         qx[i] = get_num();
61         qy[i] = get_num();
62         q[qx[i]].push_back(i);
63         q[qy[i]].push_back(i);
64     }
65     dfs(s);
66     for(i = 1; i <= m; i++) printf("%d\n", ans[i]);
67     return 0;
68 }