小机房的树 codevs 2370

#include<cstdio>
#include<algorithm>

using namespace std;

struct node {
    int to,dis,next;
};
struct node edge[50000*2+1];

int n,m,head[50001],num=0,dfn[50001],flag=0;

char ch;

inline void read_int(int &x)
{
    x=0;ch=getchar();
    while(ch>‘9‘||ch<‘0‘) ch=getchar();
    while(ch>=‘0‘&&ch<=‘9‘){x=x*10+(int)(ch-‘0‘);ch=getchar();}
}

inline void edge_add(int from,int to,int dis)
{
    num++;
    edge[num].to=to;
    edge[num].dis=dis;
    edge[num].next=head[from];
    head[from]=num;
}

void dfs(int now)
{
    dfn[now]=++flag;
    for(int i=head[now];i;i=edge[i].next) if(!dfn[edge[i].to]) dfs(edge[i].to);
}

int lca(int now_1,int now_2)
{
    int dis_1=0,dis_2=0;
    while(dfn[now_2]>dfn[now_1])
    {
        for(int i=head[now_2];i;i=edge[i].next)
        {
            if(dfn[edge[i].to]<dfn[now_2])
            {
                now_2=edge[i].to;
                dis_2+=edge[i].dis;
            }
        }
    }
    while(dfn[now_1]>dfn[now_2])
    {
        for(int i=head[now_1];i;i=edge[i].next)
        {
            if(dfn[edge[i].to]<dfn[now_1])
            {
                now_1=edge[i].to;
                dis_1+=edge[i].dis;
            }
        }
    }
    return dis_1+dis_2;
}

int main()
{
    read_int(n);
    int from,to,dis;
    for(int i=1;i<n;i++)
    {
        read_int(from),read_int(to),read_int(dis);
        edge_add(from,to,dis);
        edge_add(to,from,dis);
    }
    read_int(m);
    dfs(1);
    for(int i=1;i<=m;i++)
    {
        read_int(from),read_int(to);
        if(dfn[from]>dfn[to]) swap(from,to);
        printf("%d\n",lca(from,to));
    }
    return 0;
}