树剖指针版lca之小机房的树

题目>>http://codevs.cn/problem/2370/
变量名及其他参照：http://blog.csdn.net/qq_36519085/article/details/77187441

#include<iostream>#include<cstdio>#include<cstring>#include<algorithm>#include<cmath>using namespace std;const int MAXN = 4e5 + 5;int n,m,firs[MAXN],nex[MAXN],cnt = 0,num = 0,a,b,c;struct zt{    int f,t,v;}road[MAXN];struct zz{    int num,deep,dis,sz;    zz *fa,*son,*top;}tree[MAXN];zz *fin[MAXN];void build(int f,int t,int v){    road[++cnt] = (zt){f,t,v};    nex[cnt] = firs[f];    firs[f] = cnt;}void build_tree(zz *root,int x,int f,int v){    root->num = x;root->dis = v;fin[x] = root;    root->deep = root->fa->deep + 1;    root->sz = 1;    for(int i = firs[x];i != -1;i = nex[i])    {        int u = road[i].t;        if(u != f)        {            tree[++num].fa = root;            build_tree(&tree[num],u,x,v + road[i].v);            root->sz += fin[u]->sz;            if(!root->son||root->son->sz < fin[u]->sz) root->son = fin[u];        }    }}void dfs(zz *root,zz *j){    root->top = j;    if(!root->son) return;    if(root->son) dfs(root->son,j);    for(int i = firs[root->num];i != -1;i = nex[i])    {        int v = road[i].t;        if(v != root->son->num&&v != root->fa->num)            dfs(fin[v],fin[v]);    }}int lca(int a,int b){    while(fin[a]->top != fin[b]->top)    {        if(fin[a]->top->deep > fin[b]->top->deep)            a = fin[a]->top->fa->num;        else b = fin[b]->top->fa->num;    }    return fin[a]->deep > fin[b]->deep ? b : a;}int main(){    scanf("%d",&n);    for(int i = 0;i <= n;i ++) firs[i] = -1;    for(int i = 1;i < n;i ++)    {        scanf("%d%d%d",&a,&b,&c);        build(a,b,c);        build(b,a,c);    }//以上为基本建图     tree[0].fa = &tree[0];//确立根节点的父亲     build_tree(tree,0,0,0);    dfs(tree,tree);    scanf("%d",&m);    for(int i = 1;i <= m;i ++)    {        scanf("%d%d",&a,&b);        cout<<(fin[a]->dis + fin[b]->dis - (fin[lca(a,b)]->dis << 1))<<'\n';    }}