BZOJ 1602 USACO 2008 Oct. 牧场行走

#include<cstdio>
#include<algorithm>
#define N (1010)
#define rg register
#define LL long long
using namespace std;
int n,m,root,cnt,tot,dep[N],in[N],out[N],fa[N],last[N],a[N][N];
LL ans=0;
struct edge{
	int to,pre,dis;	
}e[N<<1];
inline int read(){
	int k=0,f=1; char c=getchar();
	while(c<‘0‘||c>‘9‘)c==‘-‘&&(f=-1),c=getchar();
	while(‘0‘<=c&&c<=‘9‘)k=k*10+c-‘0‘,c=getchar();
	return k*f;
}
inline void add(int x,int y,int z){e[++tot]=(edge){y,last[x],z}; last[x]=tot;}
void dfs(int x,int father){
	in[x]=++cnt; dep[x]=dep[father]+1;
	for(rg int i=last[x],to;i;i=e[i].pre) if((to=e[i].to)!=father) dfs(to,fa[to]=x);
	out[x]=++cnt;
}
inline bool IN(int x,int y){
	if(in[y]<=in[x]&&out[x]<=out[y]) return 1;
	return 0;
}
int main(){
	n=read(); m=read();
	for(rg int i=1,u,v,dis;i<n;i++){
		u=read(),v=read(),dis=read();
		add(u,v,dis),add(v,u,dis);
		a[u][v]=a[v][u]=dis;
	}
	dfs(1,0);
	//for(int i=1;i<=n;i++) printf("%d %d\n",in[i],out[i]);
	for(rg int i=1,x,y;i<=m;i++){
		x=read(); y=read(); ans=0;
		if(dep[x]<dep[y]) swap(x,y);
		while(!IN(y,x)) ans+=a[x][fa[x]],x=fa[x];
		while(x!=y) ans+=a[y][fa[y]],y=fa[y];
		printf("%lld\n",ans);
	}
	return 0;
}