46 lines
1.1 KiB
C++
46 lines
1.1 KiB
C++
#include<bits/stdc++.h>
|
|
using namespace std;
|
|
int n, m, s;
|
|
vector<int> fri[500005];
|
|
int fa[500005][25];
|
|
int dep[500005];
|
|
void dfs(int now, int from = -1) {
|
|
for(int i = 1; i <= 24; ++i) {
|
|
fa[now][i] = fa[fa[now][i - 1]][i - 1];
|
|
}
|
|
for(int i : fri[now]) {
|
|
if(i == from) continue;
|
|
dep[i] = dep[now] + 1;
|
|
fa[i][0] = now;
|
|
dfs(i, now);
|
|
}
|
|
}
|
|
int lca(int a, int b) {
|
|
if(dep[a] < dep[b]) swap(a, b);
|
|
for(int i = 24; i >= 0 && dep[a] > dep[b]; --i) {
|
|
if(a == b) return a;
|
|
if(dep[fa[a][i]] >= dep[b] && dep[a] >= (1 << i)) a = fa[a][i];
|
|
if(a == b) return a;
|
|
}
|
|
if(a == b) return a;
|
|
for(int i = 24; i >= 0; --i) {
|
|
if(fa[a][i] != fa[b][i] && dep[a] >= (1 << i)) a = fa[a][i], b = fa[b][i];
|
|
}
|
|
if(a != b) a = fa[a][0];
|
|
return a;
|
|
}
|
|
int main() {
|
|
scanf("%d%d%d", &n, &m, &s);
|
|
for(int i = 1, u, v; i < n; ++i) {
|
|
scanf("%d%d", &u, &v);
|
|
fri[u].push_back(v);
|
|
fri[v].push_back(u);
|
|
}
|
|
dfs(s);
|
|
while(m--) {
|
|
int a, b;
|
|
scanf("%d%d", &a, &b);
|
|
printf("%d\n", lca(a, b));
|
|
}
|
|
return 0;
|
|
} |