题意：一棵树，给两个点，求树上有多少点到他俩距离相等

倍增lca，分好多情况讨论。。

#include
    
     #include
     
      #include
      
       #include
       
        #include
        
         #define N 100500using namespace std;int e=1,head[N];struct edge{    int u,v,next;}ed[2*N];void add(int u,int v){    ed[e].u=u;ed[e].v=v;    ed[e].next=head[u];    head[u]=e++;}int n,m;int dep[N],fa[N][22],size[N];void dfs(int x){    size[x]=1;    for(int i=1;(1<
         
          <=dep[x];i++) fa[x][i]=fa[fa[x][i-1]][i-1]; for(int i=head[x];i;i=ed[i].next){ int v=ed[i].v; if(v==fa[x][0])continue; fa[v][0]=x;dep[v]=dep[x]+1; dfs(v); size[x]+=size[v]; }}int getlca(int x,int y){ if(dep[x]
          
           =dep[y]){ x=fa[x][i]; } if(x==y) return x; for(int i=20;~i;i--) if(fa[x][i]!=fa[y][i]){ x=fa[x][i];y=fa[y][i]; } return fa[x][0];}int find(int x,int y){ int d=dep[x]-y; for(int i=20;~i;i--) if(dep[fa[x][i]]>=d) x=fa[x][i]; return x;}int main(){ scanf("%d",&n);int u,v; for(int i=1;i
           
            dep[v])swap(u,v); int lca=getlca(v,u),mid,len; if(lca==u){ len=dep[v]-dep[u]; if(len%2==1){printf("%d\n",0);continue;} else{ mid=find(v,len/2); printf("%d\n",size[mid]-size[find(v,dep[v]-dep[mid]-1)]); continue; } } len=dep[u]+dep[v]-2*dep[lca]; if(len%2==1){printf("%d\n",0);continue;} else{ mid=find(v,len/2); if(mid==lca){ printf("%d\n",n-size[find(u,dep[u]-dep[lca]-1)]-size[find(v,dep[v]-dep[lca]-1)]); continue; } else{ printf("%d\n",size[mid]-size[find(v,dep[v]-dep[mid]-1)]); continue; } } } return 0;}