CodeForces 519E 树形DP A and B and Lecture Rooms

给出一棵树，有若干次询问，每次询问距两个点u, v距离相等的点的个数。

情况还挺多的，少侠不妨去看官方题解。^_^

 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <algorithm>
 #include <vector>
 using namespace std;

 const int maxn =  + ;

 int n, Q;
 vector<int> G[maxn];

 int L[maxn];
 int fa[maxn];
 int sz[maxn];

 void dfs(int u)
 {
     sz[u] = ;
     for(int i = ; i < G[u].size(); i++)
     {
         int v = G[u][i];
         if(v == fa[u]) continue;
         fa[v] = u;
         L[v] = L[u] + ;
         dfs(v);
         sz[u] += sz[v];
     }
 }

 const int logmaxn = ;
 int anc[maxn][logmaxn];

 int ancestor(int a, int x)
 {
     if(!x) return a;
     for(int i = ; ( << i) <= x; i++)
         if(x & ( << i)) a = anc[a][i];

     return a;
 }

 int LCA(int p, int q)
 {
     if(L[p] < L[q]) swap(p, q);
     int log;
     for(log = ; ( << log) <= L[p]; log++); log--;
     for(int i = log; i >= ; i--)
         if(L[p] - ( << i) >= L[q]) p = anc[p][i];
     if(p == q) return p;
     for(int i = log; i >= ; i--)
         if(anc[p][i] && anc[p][i] != anc[q][i])
             p = anc[p][i], q = anc[q][i];
     return fa[p];
 }

 int main()
 {
     //freopen("in.txt", "r", stdin);

     scanf("%d", &n);
     for(int i = ; i < n; i++)
     {
         int u, v; scanf("%d%d", &u, &v);
         G[u].push_back(v);
         G[v].push_back(u);
     }

     dfs();

     for(int i = ; i <= n; i++) anc[i][] = fa[i];
     for(int j = ; ( << j) < n; j++)
         for(int i = ; i <= n; i++) if(anc[i][j-])
             anc[i][j] = anc[anc[i][j-]][j-];

     scanf("%d", &Q);
     while(Q--)
     {
         int u, v; scanf("%d%d", &u, &v);

         if(u == v) { printf("%d\n", n); continue; }

         int l = LCA(u, v);

         if((L[u] + L[v] - L[l] * ) & ) { puts(""); continue; }

         if(L[u] == L[v])
         {
             int t = L[u] - L[l];
             int uu = ancestor(u, t - ), vv = ancestor(v, t - );
             printf("%d\n", n - sz[uu] - sz[vv]);
             continue;
         }

         if(L[u] < L[v]) swap(u, v);
         int t = L[u] + L[v] - L[l] * ;
         int p1 = ancestor(u, t / );
         int p2 = ancestor(u, t /  - );
         printf("%d\n", sz[p1] - sz[p2]);
     }

     return ;
 }

代码君