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  1. #include <bits/stdc++.h>
  2.  
  3. #define ll long long
  4. #define el cout << '\n'
  5.  
  6. using namespace std;
  7.  
  8. const int maxn = 5e2;
  9. const int MOD = 1e9 +7;
  10.  
  11. int n;
  12. string s;
  13. ll dp[maxn + 10][maxn + 10], C[maxn + 10][maxn + 10];
  14.  
  15. int main()
  16. {
  17.     ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  18.     if (fopen("EMPTY_STRING.INP", "r"))
  19.     {
  20.         freopen("EMPTY_STRING.INP", "r", stdin);
  21.         freopen("EMPTY_STRING.OUT", "w", stdout);
  22.     }
  23.  
  24.     cin >> s;
  25.     n = s.size();
  26.     s = ' ' + s;
  27.     for (int i = 0; i <= n + 1; i++)
  28.     {
  29.         C[0][i] = 1;
  30.         dp[i][i - 1] = 1;
  31.     }
  32.     for (int j = 1; j <= n; j++)
  33.         for (int i = 1; i <= n; i++)
  34.             C[i][j] = (C[i][j - 1] + C[i - 1][j - 1]) % MOD;
  35.     for (int i = n; i >= 1; i--)
  36.         for (int j = i; j <= n; j++)
  37.         {
  38.             int len = j - i + 1;
  39.             if (len & 1) continue;
  40.             for (int k = i; k <= j; k++)
  41.             {
  42.                 int lenik = k - i + 1;
  43.                 if (lenik & 1) continue;
  44.                 if (s[i] == s[k])
  45.                 {
  46.                     dp[i][j] += C[lenik/2][len/2] * dp[i + 1][k - 1] % MOD * dp[k + 1][j];
  47.                     dp[i][j] %= MOD;
  48.                 }
  49.             }
  50.         }
  51.     cout << dp[1][n];
  52. }
  53.  
Success #stdin #stdout 0.01s 5296KB
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1
https://ideone.com/2eXooH
language:
C++14 (gcc 8.3)
created:
13 days ago
visibility:
public

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