【LCA】 HDOJ How far away ？

求出LCA，然后ans = dis[u] + dis[v] - 2*dis[ancestor[v]]。。。

#include <iostream>  
#include <queue>  
#include <stack>  
#include <map>  
#include <set>  
#include <bitset>  
#include <cstdio>  
#include <algorithm>  
#include <cstring>  
#include <climits>  
#include <cstdlib>
#include <cmath>
#include <time.h>
#define maxn 400005
#define maxm 400005
#define eps 1e-10
#define mod 1000000007
#define INF 999999999
#define lowbit(x) (x&(-x))
#define mp mark_pair
#define ls o<<1
#define rs o<<1 | 1
#define lson o<<1, L, mid  
#define rson o<<1 | 1, mid+1, R  
//typedef vector<int>::iterator IT;
typedef long long LL;
//typedef int LL;
using namespace std;
LL qpow(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base;base=base*base;b/=2;}return res;}
LL powmod(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base%mod;base=base*base%mod;b/=2;}return res;}
void scanf(int &__x){__x=0;char __ch=getchar();while(__ch==' '||__ch=='\n')__ch=getchar();while(__ch>='0'&&__ch<='9')__x=__x*10+__ch-'0',__ch = getchar();}
LL gcd(LL _a, LL _b){if(!_b) return _a;else return gcd(_b, _a%_b);}
// head

struct qu
{
	int a, b, pa;
}q[maxn];
int h[maxn], next[maxm], v[maxm], cost[maxm];
int H[maxn], NEXT[maxm], V[maxm], id[maxm];
int f[maxn], dis[maxn], vis[maxn], ancestor[maxn];
int cnt, CNT, n, m;

void init(void)
{
	cnt = CNT = dis[1] = 0;
	memset(h, -1, sizeof h);
	memset(H, -1, sizeof H);
	memset(vis, 0, sizeof vis);
}
void addedges(int a, int b, int c)
{
	next[cnt] = h[a], h[a] = cnt, v[cnt] = b, cost[cnt] = c, cnt++;
}
void Addedges(int A, int B, int c)
{
	NEXT[CNT] = H[A], H[A] = CNT, V[CNT] = B, id[CNT] = c, CNT++;
}
int find(int u)
{
	return u == f[u] ? f[u] : find(f[u]);
}
void merge(int a, int b)
{
	int aa = f[a], bb = f[b];
	f[aa] = bb;
}
void read(void)
{
	int a, b, c;
	scanf("%d%d", &n, &m);
	for(int i = 0; i <= n; i++) f[i] = i;
	for(int i = 1; i < n; i++) {
		scanf(a), scanf(b), scanf(c);
		addedges(a, b, c);
		addedges(b, a, c);
	}
	for(int i = 1; i <= m; i++) {
		scanf(q[i].a), scanf(q[i].b);
		Addedges(q[i].a, q[i].b, i);
		Addedges(q[i].b, q[i].a, i);
	}
}
void lca(int u)
{
	vis[u] = 1;
	ancestor[u] = u;
	for(int e = h[u]; ~e; e = next[e]) if(!vis[v[e]]) {
		dis[v[e]] = dis[u] + cost[e];
		lca(v[e]);
		merge(u, v[e]);
		ancestor[find(u)] = u;
	}
	for(int e = H[u]; ~e; e = NEXT[e]) if(vis[V[e]])
		q[id[e]].pa = ancestor[find(V[e])];
}
void work(void)
{
	lca(1);
	for(int i = 1; i <= m; i++)
		printf("%I64d\n", (LL)dis[q[i].a] + dis[q[i].b] - (LL)2*dis[q[i].pa]);
}
int main(void)
{
	int _;
	while(scanf("%d", &_)!=EOF) {
		while(_--) {
			init();
			read();
			work();
		}
	}
	return 0;
}