How far away ？ LCA求树上两点距离

How far away ？

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 22976    Accepted Submission(s): 9078

Problem Description

There are n houses in the village and some bidirectional roads connecting them. Every day peole always like to ask like this "How far is it if I want to go from house A to house B"? Usually it hard to answer. But luckily int this village the answer is always unique, since the roads are built in the way that there is a unique simple path("simple" means you can't visit a place twice) between every two houses. Yout task is to answer all these curious people.

 

Input

First line is a single integer T(T<=10), indicating the number of test cases.
  For each test case,in the first line there are two numbers n(2<=n<=40000) and m (1<=m<=200),the number of houses and the number of queries. The following n-1 lines each consisting three numbers i,j,k, separated bu a single space, meaning that there is a road connecting house i and house j,with length k(0<k<=40000).The houses are labeled from 1 to n.
  Next m lines each has distinct integers i and j, you areato answer the distance between house i and house j.

 

Output

For each test case,output m lines. Each line represents the answer of the query. Output a bland line after each test case.

 

Sample Input

2
3 2
1 2 10
3 1 15
1 2
2 3

2 2
1 2 100
1 2
2 1

 

Sample Output

10
25
100
100

 

Source

ECJTU 2009 Spring Contest

 

 #include <cstdio>
 #include <cstring>
 #include <queue>
 #include <cmath>
 #include <algorithm>
 #include <set>
 #include <iostream>
 #include <map>
 #include <stack>
 #include <string>
 #include <vector>
 #define  pi acos(-1.0)
 #define  eps 1e-6
 #define  fi first
 #define  se second
 #define  lson l,m,rt<<1
 #define  rson m+1,r,rt<<1|1
 #define  bug         printf("******\n")
 #define  mem(a,b)    memset(a,b,sizeof(a))
 #define  fuck(x)     cout<<"["<<x<<"]"<<endl
 #define  f(a)        a*a
 #define  sf(n)       scanf("%d", &n)
 #define  sff(a,b)    scanf("%d %d", &a, &b)
 #define  sfff(a,b,c) scanf("%d %d %d", &a, &b, &c)
 #define  sffff(a,b,c,d) scanf("%d %d %d %d", &a, &b, &c, &d)
 #define  pf          printf
 #define  FRE(i,a,b)  for(i = a; i <= b; i++)
 #define  FREE(i,a,b) for(i = a; i >= b; i--)
 #define  FRL(i,a,b)  for(i = a; i < b; i++)
 #define  FRLL(i,a,b) for(i = a; i > b; i--)
 #define  FIN         freopen("DATA.txt","r",stdin)
 #define  gcd(a,b)    __gcd(a,b)
 #define  lowbit(x)   x&-x
 #pragma  comment (linker,"/STACK:102400000,102400000")
 using namespace std;
 typedef long long LL;
 typedef unsigned long long ULL;
 const int maxn = 1e5 + ;
 int _pow[maxn], dep[maxn], dis[maxn], vis[maxn], ver[maxn];
 int tot, head[maxn], dp[maxn * ][], k, first[maxn];
 struct node {
     int u, v, w, nxt;
 } edge[maxn << ];
 void init() {
     tot = ;
     mem(head, -);
 }
 void add(int u, int v, int w) {
     edge[tot].v = v, edge[tot].u = u;
     edge[tot].w = w, edge[tot].nxt = head[u];
     head[u] = tot++;
 }
 void dfs(int u, int DEP) {
     vis[u] = ;
     ver[++k] = u;
     first[u] = k;
     dep[k] = DEP;
     for (int i = head[u]; ~i; i = edge[i].nxt) {
         if (vis[edge[i].v]) continue;
         int v = edge[i].v, w = edge[i].w;
         dis[v] = dis[u] + w;
         dfs(v, DEP + );
         ver[++k] = u;
         dep[k] = DEP;
     }
 }
 void ST(int len) {
     int K = (int)(log((double)len) / log(2.0));
     for (int i =  ; i <= len ; i++) dp[i][] = i;
     for (int j =  ; j <= K ; j++) {
         for (int i =  ; i + _pow[j] -  <= len ; i++) {
             int a = dp[i][j - ], b = dp[i + _pow[j - ]][j - ];
             if (dep[a] < dep[b]) dp[i][j] = a;
             else dp[i][j] = b;
         }
     }
 }
 int RMQ(int x, int y) {
     int K = (int)(log((double)(y - x + )) / log(2.0));
     int a = dp[x][K], b = dp[y - _pow[K] + ][K];
     if (dep[a] < dep[b]) return a;
     else return b;
 }
 int LCA(int u, int v) {
     int x = first[u], y = first[v];
     if (x > y) swap(x, y);
     int ret = RMQ(x, y);
     return ver[ret];
 }
 int main() {
     for (int i =  ; i <  ; i++) _pow[i] = ( << i);
     int t;
     sf(t);
     while(t--) {
         int n, q;
         init();
         sff(n, q);
         mem(vis, );
         for (int i =  ; i < n ; i++) {
             int u, v, w;
             sfff(u, v, w);
             add(u, v, w);
             add(v, u, w);
         }
         k = , dis[] = ;
         dfs(, );
         ST( * n - );
         while(q--) {
             int u, v;
             sff(u, v);
             int lca = LCA(u, v);
             printf("%d\n", dis[u] + dis[v] -  * dis[lca]);
         }
     }
     return  ;
 }