mirror of
https://git.sb/baoshuo/OI-codes.git
synced 2024-11-30 16:36:26 +00:00
63 lines
1.3 KiB
C++
63 lines
1.3 KiB
C++
#pragma GCC optimize("Ofast")
|
|
|
|
#include <bits/stdc++.h>
|
|
|
|
using namespace std;
|
|
|
|
int n, m, s, root, a, b, dep[500005], fa[500005][20];
|
|
vector<int> tr[500005];
|
|
|
|
void bfs(int root) {
|
|
memset(dep, 0x3f, sizeof(dep));
|
|
dep[0] = 0;
|
|
dep[root] = 1;
|
|
queue<int> q;
|
|
q.push(root);
|
|
while (!q.empty()) {
|
|
int t = q.front();
|
|
q.pop();
|
|
for (int i : tr[t]) {
|
|
if (dep[i] > dep[t] + 1) {
|
|
dep[i] = dep[t] + 1;
|
|
q.push(i);
|
|
fa[i][0] = t;
|
|
for (int k = 1; k <= 19; k++) {
|
|
fa[i][k] = fa[fa[i][k - 1]][k - 1];
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
int lca(int a, int b) {
|
|
if (dep[a] < dep[b]) swap(a, b);
|
|
for (int k = 19; k >= 0; k--) {
|
|
if (dep[fa[a][k]] >= dep[b]) {
|
|
a = fa[a][k];
|
|
}
|
|
}
|
|
if (a == b) return a;
|
|
for (int k = 19; k >= 0; k--) {
|
|
if (fa[a][k] != fa[b][k]) {
|
|
a = fa[a][k];
|
|
b = fa[b][k];
|
|
}
|
|
}
|
|
return fa[a][0];
|
|
}
|
|
|
|
int main() {
|
|
scanf("%d%d%d", &n, &m, &root);
|
|
for (int i = 1; i < n; i++) {
|
|
scanf("%d%d", &a, &b);
|
|
tr[a].push_back(b);
|
|
tr[b].push_back(a);
|
|
}
|
|
bfs(root);
|
|
for (int i = 0; i < m; i++) {
|
|
scanf("%d%d", &a, &b);
|
|
printf("%d\n", lca(a, b));
|
|
}
|
|
return 0;
|
|
}
|