Codeforces 519E A and B and Lecture Rooms

http://codeforces.com/contest/519/problem/E

题意:

给出一棵树和m次询问，每次询问给出两个点，求出到这两个点距离相等的点的个数。

思路:

lca...然后直接判就好了，挂dp标签的人是什么心态。。

 #include<cstdio>
 #include<cmath>
 #include<algorithm>
 #include<cstring>
 #include<iostream>
 int tot,go[],first[],next[];
 int son[],fa[][];
 int deep[];
 int n,bin[];
 int read(){
     int t=,f=;char ch=getchar();
     while (ch<''||ch>''){if (ch=='-') f=-;ch=getchar();}
     while (''<=ch&&ch<=''){t=t*+ch-'';ch=getchar();}
     return t*f;
 }
 void insert(int x,int y){
     tot++;
     go[tot]=y;
     next[tot]=first[x];
     first[x]=tot;
 }
 void add(int x,int y){
     insert(x,y);insert(y,x);
 }
 void dfs(int x,int f){
     son[x]=;
     for (int i=;i<=;i++)
      fa[x][i]=fa[fa[x][i-]][i-];
     for (int i=first[x];i;i=next[i]){
         int pur=go[i];
         if (pur==f) continue;
         deep[pur]=deep[x]+;
         fa[pur][]=x;
         dfs(pur,x);
         son[x]+=son[pur];
     }
 }
 int lca(int x,int y){
     if (deep[x]<deep[y]) std::swap(x,y);
     int t=deep[x]-deep[y];
     for (int i=;i<=;i++)
      if (t&bin[i])
       x=fa[x][i];
     if (x==y) return x;
     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;
     else return fa[x][];
 }
 void up(int &x,int dep){
     int t=deep[x]-dep;
     for (int i=;i<=;i++)
      if (t&bin[i])
       x=fa[x][i];
 }
 void work(int x,int y){
     int t=lca(x,y);
     int len=deep[x]-deep[t]++deep[y]-deep[t]+-;
     if (len%==){
         printf("0\n");
         return;
     }
     if (x==y){
         printf("%d\n",n);
         return;
     }
     if (t==x||t==y){
         if (t==x) std::swap(x,y);
         int tt=x;
         up(tt,deep[tt]-len/);
         up(x,deep[tt]+);
         printf("%d\n",son[tt]-son[x]);
     }else{
         if (deep[x]<deep[y]) std::swap(x,y);
         if (deep[x]==deep[y]){
             up(x,deep[t]+);
             up(y,deep[t]+);
             printf("%d\n",n-son[x]-son[y]);
         }else{
             int tt=x;
             up(tt,deep[tt]-len/);
             up(x,deep[tt]+);
             printf("%d\n",son[tt]-son[x]);
         }
     }
 }
 int main(){
     n=read();bin[]=;for (int i=;i<=;i++) bin[i]=bin[i-]*;
     for (int i=;i<n;i++){
         int x=read(),y=read();
         add(x,y);
     }
     dfs(,);
     int T=read();
     while (T--){
         int x=read(),y=read();
         work(x,y);
     }
     return ;
 }