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1471.cpp
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1471.cpp
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/*
* Author : Nguyen Le Minh
* Group : N3251
* Date : 9/4/2021
* Problem : 1471
*/
#include <bits/stdc++.h>
using namespace std;
const int MAXLOG = 16;
vector <vector<pair<int,int>>> adj;
vector <vector< int > > dp;
vector < int > dist;
vector < int > h;
int n,q;
void dfs(int u,int par){
dp[0][u] = par;
for(auto [v,w] : adj[u]){
if(v != par){
h[v] = h[u] + 1;
dist[v] = dist[u] + w;
dfs(v,u);
}
}
}
int getLca(int u,int v){
if(h[u] < h[v]){
swap(u,v);
}
for(int j = MAXLOG;~j;--j){
if(h[dp[j][u]] >= h[v]){
u = dp[j][u];
}
}
if(u == v){
return u;
}
for(int j = MAXLOG;j > -1;--j){
if(dp[j][u] != dp[j][v]){
u = dp[j][u];
v = dp[j][v];
}
}
return dp[0][u];
}
int getDist(int u,int v){
return dist[u] + dist[v] - 2 * dist[getLca(u,v)];
}
void solve(){
cin>>n;
adj.resize(n + 2,vector < pair < int,int > > ());
for(int i = 1;i < n;++i){
int u,v,w; cin>>u>>v>>w;
adj[u].emplace_back(make_pair(v,w));
adj[v].emplace_back(make_pair(u,w));
}
dist.resize(n + 2,0);
h.resize(n + 2,0);
dp.resize(MAXLOG + 2,vector < int > (n + 2,0));
dfs(0,0);
for(int j = 1;j <= MAXLOG;++j){
for(int i = 0;i < n;++i){
dp[j][i] = dp[j - 1][dp[j - 1][i]];
}
}
cin>>q;
while(q--){
int u,v; cin>>u>>v;
cout<<getDist(u,v)<<'\n';
}
}
int main(){
ios_base::sync_with_stdio(false); cin.tie(nullptr);
solve();
return 0;
}