[BZOJ1602] [Usaco2008 OCT] Ranch walking (LCA)

Description

N Cattle (2<=n<=1000) Others are labeled 1 to N, grazing on n blocks of land that are also labeled 1 to N, and the first cattle graze on the block I ranch. This n block of land is connected by a n-1 strip. The cow can walk on the edge, the section I is connected to the Ai,bi ranch, and the length of the first edge is Li (1<=li<=10000). These sides are arranged so that any two cows can reach through these sides, so this is a tree. These cows are very sociable and often visit each other, and they want you to help them calculate the distance between the 1<=q<=1000 and the cows.

Input

* First line: Two integers separated by a space: N and Q

* Line two to Nth: line i+1 has two integers separated by spaces: Ai,bi,li

* Line n+1 to n+q: Each line has two spaces separated by an integer: P1,p2, which indicates the number of two cows.

Output

* Line 1th to line Q: Output one number per line, indicating the distance between the two cows.

Sample Input4 2
2 1 2
4 3 2
1 4 3
1 2
3 2
Sample Output2
7
HINTSource

Qualifying Tournament

Solution

Naked LCA, people who can't read the code are　　　　

1#include <bits/stdc++.h>2 using namespacestd;3 structEdge4 {5     intV, W, NXT;6}e[2005];7 structQuery8 {9     intu, V, NXT;Ten}q[2005]; One intefst[1005], qfst[1005], fa[1005], lca[1005], dis[1005]; A BOOLvis[1005]; -   - voidAddedge (intIintUintVintW) the { -E[i] = (edge) {V, W, Efst[u]}, efst[u] =i; - } -   + voidAddQuery (intIintUintv) - { +Q[i] = (query) {u, V, Qfst[u]}, qfst[u] =i; A } at   - intGet_dis (inti) - { -     returnDis[q[i <<1].U] + dis[q[i <<1].V]-2*Dis[lca[i]]; - } -   in intGETFA (intx) - { to     returnFA[X] = x = = Fa[x]?X:GETFA (fa[x]); + } -   the voidTarjan (intu) * { $Fa[u] = u, vis[u] =true;Panax Notoginseng      for(inti = Efst[u]; I i =e[i].nxt) -         if(!VIS[E[I].V]) the         { +DIS[E[I].V] = Dis[u] +E[I].W; A Tarjan (E[I].V); theFA[E[I].V] =u; +         } -      for(inti = Qfst[u]; I i =q[i].nxt) $     { $         intv = q[i].u = = u?q[i].v:q[i].u; -         if(Vis[v]) lca[i >>1] =GETFA (Fa[v]); -     } the } -  Wuyi intMain () the { -     intN, q, U, V, W; WuCIN >> N >>Q; -      for(inti =1; I < n; i++) About     { $cin >> u >> v >>W; -Addedge (i <<1, U, V, W); -Addedge (i <<1|1, V, u, W); -     } A      for(inti =1; I <= Q; i++) +     { theCIN >> U >>v; -AddQuery (i <<1, u, v); $AddQuery (i <<1|1, V, u); the     } theTarjan (1); the      for(inti =1; I <= Q; i++) thecout << Get_dis (i) <<Endl; -     return 0; in}

View Code

[BZOJ1602] [Usaco2008 OCT] Ranch walking (LCA)