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| #include <cstdio>
#include <algorithm>
#include <cmath>
const int maxn = 5e5 + 5;
using namespace std;
struct E{
int to, nxt;
}e[maxn << 1];
int head[maxn], tot = 0;
void addedge(int u, int v){
e[++tot].to = v, e[tot].nxt = head[u];
head[u] = tot;
}
int Min[maxn << 1][25], tdx = 0;
int link[maxn], dep[maxn], x[maxn << 1][25];
void dfs(int cur, int fa){
dep[cur] = dep[fa] + 1;
Min[++tdx][0] = dep[cur];
x[tdx][0] = cur;
for (int i = head[cur]; i; i = e[i].nxt){
int v = e[i].to;
if (v != fa){
dfs(v, cur);
Min[++tdx][0] = dep[cur];
x[tdx][0] = cur;
}
}
link[cur] = tdx;
}
void ins(){
for (int j = 1; j <= 24; j++)
for (int i = 1; i + (1 << j) - 1 <= tdx; i++)
if (Min[i][j - 1] < Min[i + (1 << (j - 1))][j - 1]) x[i][j] = x[i][j - 1], Min[i][j] = Min[i][j - 1];
else x[i][j] = x[i + (1 << (j - 1))][j - 1], Min[i][j] = Min[i + (1 << (j - 1))][j - 1];
}
int Query(int l, int r){
int k = (int)log2(r - l + 1);
if (Min[l][k] < Min[r - (1 << k) + 1][k]) return x[l][k];
else return x[r - (1 << k) + 1][k];
}
int n, Q, rt;
int main(){
scanf("%d%d%d", &n, &Q, &rt);
for (int u, v, i = 1; i < n; i++){
scanf("%d%d", &u, &v);
addedge(u, v); addedge(v, u);
}
dfs(rt, 0);
ins();
while (Q--){
int u, v; scanf("%d%d", &u, &v);
if (link[u] > link[v]) swap(u, v);
printf("%d\n", Query(link[u], link[v]));
}
return 0;
}
|