POJ 1986 裸的LCA

思路：搞了一发链剖

//By SiriusRen
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
#define N 88888
int n,m,first[N],next[N],v[N],w[N],tot,xx,yy,zz,k;
int top[N],size[N],deep[N],son[N],fa[N],weight[N];
void add(int x,int y,int z){
    w[tot]=z,v[tot]=y;
    next[tot]=first[x],first[x]=tot++;
}
void dfs(int x){
    size[x]=1;
    for(int i=first[x];~i;i=next[i])
        if(v[i]!=fa[x]){
            fa[v[i]]=x;
            deep[v[i]]=deep[x]+1;
            weight[v[i]]=weight[x]+w[i];
            dfs(v[i]);
            size[x]+=size[v[i]];
            if(size[son[x]]<size[v[i]])son[x]=v[i];
        }
}
void dfs2(int x,int tp){
    top[x]=tp;
    if(son[x])dfs2(son[x],tp);
    for(int i=first[x];~i;i=next[i]){
        if(v[i]!=fa[x]&&v[i]!=son[x]){
            dfs2(v[i],v[i]);
        }
    }
}
int lca(int x,int y){
    int fx=top[x],fy=top[y];
    while(fx!=fy){
        if(deep[fx]<deep[fy])
            swap(fx,fy),swap(x,y);
        x=fa[fx],fx=top[x];
    }
    if(deep[x]<deep[y])return x;
    return y;
}
int main(){
    memset(first,-1,sizeof(first));
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++){
        scanf("%d%d%d",&xx,&yy,&zz),getchar(),getchar(),getchar();
        add(xx,yy,zz),add(yy,xx,zz);
    }
    dfs(1),dfs2(1,1);
    scanf("%d",&k);
    for(int i=1;i<=k;i++){
        scanf("%d%d",&xx,&yy);
        printf("%d
",weight[xx]+weight[yy]-2*weight[lca(xx,yy)]);
    }
}