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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. #define task "main"
  4. #define fi first
  5. #define se second
  6. #define ll long long
  7. const int mod=1e9+7;
  8. const int maxn=1e7+5;
  9. const int base=311;
  10. ll n,k;
  11. vector<ll> g[2000000];
  12. ll dp[200000][200];
  13. ll ans=0;
  14. void dfs(ll u,ll par)
  15. {
  16.     for (int v:g[u])
  17.     {
  18.         if (v==par) continue;
  19.         dfs(v,u);
  20.         for (int i=0;i<k;i++)
  21.         {
  22.             ans += dp[u][i]*dp[v][k-i-1];
  23.         }
  24.         for (int i=1;i<=k;i++)
  25.         {
  26.             dp[u][i]+=dp[v][i-1];
  27.         }       
  28.     }
  29. }
  30. signed main()
  31. {
  32.     ios_base::sync_with_stdio(false);
  33.     cin.tie(0);
  34.     cout.tie(0);
  35.     if (fopen(task".inp","r"))
  36.     {
  37.         freopen(task".inp","r",stdin);
  38.         freopen(task".out","w",stdout);
  39.     }
  40.     cin>>n>>k;
  41.  
  42.     for (int i=1;i<=n;i++) dp[i][0]=1;
  43.     for (int i=1;i<n;i++)
  44.     {
  45.         ll u,v;
  46.         cin>>u>>v;
  47.         g[u].push_back(v);
  48.         g[v].push_back(u);
  49.     }
  50.     dfs(1,0);
  51.     cout<<ans;
  52. }
Success #stdin #stdout 0.02s 50552KB
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https://ideone.com/HShhg2
language:
C++14 (clang 8.0)
created:
1 year ago
visibility:
secret

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