LCA【bzoj3364】 [Usaco2004 Feb]Distance Queries 距离咨询

明显\(LCA\)问题。

\(Dfs\)建树之后,对于每个询问,直接求带权\(LCA\)即可

代码

#include<cstdio>
#include<iostream>
#include<cstring>
#include<cctype>
#define R register
#define N 100860
using namespace std;
inline void in(int &x)
{
int f=1;x=0;char s=getchar();
while(!isdigit(s)){if(s=='-')f=-1;s=getchar();}
while(isdigit(s)){x=x*10+s-'0';s=getchar();}
x*=f;
}
int n,m,head
,tot,now,ans,gw
[21],f
[21],q;
int depth
;
struct cod{int u,v,w;}edge[N<<2];
inline void add(int x,int y,int z)
{
edge[++tot].u=head[x];
edge[tot].v=y;
edge[tot].w=z;
head[x]=tot;
}
void dfs(int u,int fa,int dist)
{
gw[u][0]=dist;f[u][0]=fa;
depth[u]=depth[fa]+1;
for(R int i=1;(1<<i)<=depth[u];i++)
{
f[u][i]=f[f[u][i-1]][i-1];
gw[u][i]=gw[u][i-1]+gw[f[u][i-1]][i-1];
}
for(R int i=head[u];i;i=edge[i].u)
{
if(edge[i].v==fa)continue;
dfs(edge[i].v,u,edge[i].w);
}
}
inline int lca(int x,int y)
{
int res=0;
if(depth[x]>depth[y])swap(x,y);
for(R int i=17;i>=0;i--)
if(depth[x]+(1<<i)<=depth[y])
res+=gw[y][i],y=f[y][i];
if(x==y)return res;
for(R int i=17;i>=0;i--)
{
if(f[y][i]==f[x][i])continue;
res+=gw[x][i]+gw[y][i];
y=f[y][i],x=f[x][i];
}
return res+gw[y][0]+gw[x][0];
}
int main()
{
in(n),in(m);
for(R int i=1,x,y,z;i<=m;i++)
{
R char opt;
in(x),in(y),in(z);cin>>opt;
add(x,y,z);add(y,x,z);
}
dfs(1,0,0);
in(q);
for(R int l,r;q;q--)
{
in(l),in(r);
printf("%d\n",lca(l,r));
}
}