HDU 2586 How far away ？

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 using namespace std;
 5 const int MAXN=1e5+10;
 6 inline int read()
 7 {
 8     char c=getchar();int x=0,f=1;
 9     while(c<‘0‘||c>‘9‘)    {if(c==‘-‘)    f=-1;c=getchar();}
10     while(c>=‘0‘&&c<=‘9‘)    x=x*10+c-48,c=getchar();return x*f;
11 }
12 int n,m,S=1; 
13 int f[MAXN][21],deep[MAXN],g[MAXN];
14 struct node
15 {
16     int u,v,w,nxt;
17 }edge[MAXN];
18 int head[MAXN];
19 int num=1;
20 inline void add_edge(int x,int y,int z)
21 {
22     edge[num].u=x;
23     edge[num].v=y;
24     edge[num].w=z;
25     edge[num].nxt=head[x];
26     head[x]=num++;
27 }
28 void dfs(int now)
29 {
30     for(int i=head[now];i!=-1;i=edge[i].nxt)
31         if(deep[edge[i].v]==0)
32         {
33             deep[edge[i].v]=deep[now]+1;
34             f[edge[i].v][0]=now;
35             g[edge[i].v]=g[now]+edge[i].w;
36             dfs(edge[i].v);
37         }
38             
39 }
40 inline void pre()
41 {
42     for(int i=1;i<=19;i++)
43         for(int j=1;j<=n;j++)
44             f[j][i]=f[f[j][i-1]][i-1];
45 }
46 inline int LCA(int x,int y)
47 {
48     if(deep[x]<deep[y])    swap(x,y);
49     for(int i=19;i>=0;i--)
50         if(deep[f[x][i]]>=deep[y])
51             x=f[x][i];
52     if(x==y)    return x;
53 
54     for(int i=19;i>=0;i--)
55         if(f[x][i]!=f[y][i])
56             x=f[x][i],y=f[y][i];
57     return f[x][0];
58 }
59 int main()
60 {
61     int T=read();
62     while(T--)
63     {
64         n=read();m=read();
65         memset(head,-1,sizeof(head));num=1;
66         memset(f,0,sizeof(f));
67         memset(deep,0,sizeof(deep));
68         for(int i=1;i<=n-1;i++)
69         {
70             int x=read(),y=read(),z=read();
71             add_edge(x,y,z);
72             add_edge(y,x,z);
73         }
74         deep[S]=1;
75         dfs(S);pre();
76         while(m--)
77         {
78             int x=read(),y=read();
79             printf("%d\n",g[x]+g[y]-2*g[LCA(x,y)]);
80         }    
81     }
82     
83     return 0;
84 }