【題目敘述】https://cses.fi/problemset/task/1135/
#include <iostream>
#include <vector>
using namespace std;
int n, q, a, b, p[200005][20], d[200005];
vector <int> v[200005];
void dfs(int x, int pre){
for (auto i:v[x]){
if (i == pre) continue;
p[i][0] = x;
d[i] = d[x]+1;
dfs(i, x);
}
}
int solve(int a, int b){
int x = d[a], y = d[b], ret = x+y;
if (x > y){
swap(a, b);
swap(x, y);
}
y -= x;
for (int i = 0; i < 20; i++){
if (y & (1<<i)){
b = p[b][i];
}
}
if (a == b) return ret-d[a]*2;
for (int i = 19; i >= 0; i--){
if (p[a][i] != p[b][i]){
a = p[a][i];
b = p[b][i];
}
}
ret -= d[p[a][0]]*2;
return ret;
}
int main() {
cin >> n >> q;
for (int i = 2; i <= n; i++){
cin >> a >> b;
v[a].push_back(b);
v[b].push_back(a);
}
dfs(1, 0);
for (int i = 1; i < 20; i++){
for (int j = 1; j <= n; j++){
p[j][i] = p[p[j][i-1]][i-1];
}
}
while (q--){
cin >> a >> b;
cout << solve(a, b) << "\n";
}
}