HDU 2586 LCA

#include <bits/stdc++.h>

using namespace std;

const int maxn = 40000+5;
const int logmaxn =  20;
struct Edge
{
    int to,w;
};

std::vector<Edge> G[maxn];

int f[maxn],dis[maxn],deep[maxn],p[maxn][20],n;





struct LCA {

    int n;
    int fa[maxn];
    int L[maxn];
    int anc[maxn][logmaxn];

    void preprocess()
    {
        for(int i=0; i<n; i++)
        {
            anc[i][0] = fa[i];
            for(int j=1; (1<<j)<n; j++)
                anc[i][j] = -1;
        }

        for(int j=1; (1<<j)<n; j++)
        {
            for(int i=0; i<n; i++)
            {
                if(anc[i][j-1]!=-1)
                {
                    int a = anc[i][j-1];
                    anc[i][j] = anc[a][j-1];
                }
            }
        }
    }

    int query(int p,int q) {
        int log;
        if(L[p]<L[q]) swap(p,q);
        for(log = 1;(1<<log)<=L[p];log++);
        log--;

        for(int i=log;i>=0;i--) {
            if(L[p]-(1<<i)>=L[q]) {
                p = anc[p][i];
            }
        }

        if(p==q) return p;

        for(int i=log;i>=0;i--) {
            if(anc[p][i]!=-1&&anc[p][i]!=anc[q][i]) {
                p = anc[p][i];
                q = anc[q][i];
            }
        }
        return fa[p];

    }
}sol;

void dfs(int u,int pre,int t) {

    sol.L[u] = t;
    sol.fa[u] = pre;
    int num = G[u].size();

    for(int i=0;i<num;i++) {
        int v = G[u][i].to;
        if(v!=pre) {
            dis[v] = dis[u] + G[u][i].w;
            dfs(v,u,t+1);
        }
    }
}

int main(int argc, char const *argv[])
{
    //freopen("in.txt","r",stdin);
    int t;
    scanf("%d",&t);
    while(t--) {
        int n,q;
        scanf("%d%d",&n,&q);
        for(int i=0;i<n;i++)
            G[i].clear();

        sol.n = n;
        for(int i=0;i<n-1;i++) {
            int u,v,c;
            scanf("%d%d%d",&u,&v,&c);
            u--;v--;
            G[u].push_back((Edge){v,c});
            G[v].push_back((Edge){u,c});
        }
        dis[1] = 0;
        dfs(0,-1,0);
        sol.preprocess();
        while(q--) {
            int a,b;
            scanf("%d%d",&a,&b);
            a--;
            b--;
            int lca = sol.query(a,b);
            printf("%d\n",dis[a]+dis[b]-2*dis[lca]);
        }
    }
    return 0;
}