bzoj 1832: [AHOI2008]聚会

良心题2333

三个点两两求一遍就行，最小肯定是在某2个点的lca处，（肯定让第三个人去找2个人，不能让2个人一起去找第三个人233）

 #include<bits/stdc++.h>
 #define N 500005
 #define M 10000005
 #define LL long long
 #define inf 0x3f3f3f3f
 using namespace std;
 inline int ra()
 {
     int x=,f=; char ch=getchar();
     while (ch<'' || ch>'') {if (ch=='-') f=-; ch=getchar();}
     while (ch>='' && ch<='') {x=x*+ch-''; ch=getchar();}
     return x*f;
 }
 struct node{
     int to,next;
 }e[N<<];
 int head[N],cnt;
 int fa[N][],deep[N],n,m;
 void insert(int x, int y){e[++cnt].to=y; e[cnt].next=head[x]; head[x]=cnt;}
 void dfs(int x)
 {
     for (int i=; i<=; i++)
         if (deep[x]>=(<<i))
             fa[x][i]=fa[fa[x][i-]][i-];
         else break;
     for (int i=head[x];i;i=e[i].next)
     {
         if (e[i].to==fa[x][]) continue;
         fa[e[i].to][]=x;
         deep[e[i].to]=deep[x]+;
         dfs(e[i].to);
     }
 }
 int lca(int x, int y)
 {
     if (deep[x]<deep[y]) swap(x,y);
     int t=deep[x]-deep[y];
     for (int i=; (<<i)<=t ; i++)
         if (t&(<<i)) x=fa[x][i];
     for (int i=; i>=; i--)
         if (fa[x][i]!=fa[y][i])
             x=fa[x][i],y=fa[y][i];
     if (x==y) return x;
     return fa[x][];
 }
 int lca_cost(int x, int y)
 {
     int sum=;
     if (deep[x]<deep[y]) swap(x,y);
     int t=deep[x]-deep[y];
     for (int i=; (<<i)<=t ; i++)
         if (t&(<<i)) x=fa[x][i],sum+=(<<i);
     for (int i=; i>=; i--)
         if (fa[x][i]!=fa[y][i])
             x=fa[x][i],y=fa[y][i],sum+=(<<i)*;
     if (x==y) return sum;
     return sum+;
 }
 int main()
 {
     n=ra(); m=ra();
     for (int i=; i<n; i++)
     {
         int x=ra(),y=ra();
         insert(x,y); insert(y,x);
     }
     dfs();
     for (int i=; i<=m; i++)
     {
         int x=ra(),y=ra(),z=ra();
         int ans1=lca_cost(x,y)+lca_cost(lca(x,y),z);
         int ans2=lca_cost(x,z)+lca_cost(lca(x,z),y);
         int ans3=lca_cost(y,z)+lca_cost(lca(y,z),x);
         int ans=min(min(ans1,ans2),ans3);
         if (ans==ans1) printf("%d ",lca(x,y));
         else if (ans==ans2) printf("%d ",lca(x,z));
         else if (ans==ans3) printf("%d ",lca(y,z));
         printf("%d\n",ans);
     }
 }