codevs 2370

小机房的树
模板题

#include <cstdio>
#include <cmath>
#include <iostream>
#define MAXN 50010

using namespace std;


int n, x, y, v, m;
int deep[MAXN], now[MAXN];
bool vis[MAXN];
int f[MAXN][22], h[MAXN][22];
int ts, cnt;

struct E {
    int to, nxt, vl;
} es[MAXN * 2];

int read() {
    int f = 1, k = 0;
    char c = getchar();
    while (c < '0' || c > '9') {
        if(c == '-') {
            f = -1;
        }
        c = getchar();
    }
    while(c >= '0' && c <= '9') {
        k = k * 10 + c - '0';
        c = getchar();
    }
    return f * k;
}

void addedge(int a, int b, int c) {
    es[++cnt].to = b;
    es[cnt].nxt = now[a];
    es[cnt].vl = c;
    now[a] = cnt;
}

void dfs(int a) {
    vis[a] = true;
    for(int i = now[a]; i != 0; i = es[i].nxt) {
        if(!vis[es[i].to]) {
            deep[es[i].to] = deep[a] + 1;
            f[es[i].to][0] = a;
            h[es[i].to][0] = es[i].vl;
            dfs(es[i].to);
        }
    }
}

void lca_init() {
    for(int i = 1; i <= ts; i ++) {
        for(int j = 0; j <= n - 1; j ++) {
            f[j][i] = f[f[j][i - 1]][i - 1];
            h[j][i] = h[j][i - 1] + h[f[j][i - 1]][i - 1];
        }
    }
}

int lca(int a, int b) {
    int ans = 0;
    if(deep[a] < deep[b]) swap(a, b); //a的深度大
    for(int i = ts; i >= 0; i -- ) {
        if(deep[f[a][i]] >= deep[b]) {
            ans += h[a][i];
            a = f[a][i];
        }
    }
    if(a == b) return ans;
    for(int i = ts; i >= 0; i -- ) {
        if(f[a][i] != f[b][i]) {
            ans += h[a][i];
            ans += h[b][i];
            a = f[a][i];
            b = f[b][i];
        }
    }
    return ans + h[a][0] + h[b][0];
}

int main() {
    n = read();
    for(int i = 1; i < n; i ++) {
        x = read(), y = read(), v = read();
        addedge(x, y, v);
        addedge(y, x, v);
    }
    ts = (log(n) / log(2));
    deep[0] = 1;
    dfs(0);
    lca_init();
    m = read();
    for(int i = 1; i <= m; i ++) {
        x = read(), y = read();
        printf("%d\n", lca(x, y));
    }
    return 0;
}