#include "leetcode.h" #define lli long long int class Solution { public: int countOrders(int n) { lli mod = 1e9 + 7; vector dp(n + 2); dp[1] = 1; dp[2] = 6; for (lli i = 3; i <= n; i++) { lli x = 2 * i - 1; lli combs = x * (x + 1) / 2; dp[i] = (dp[i - 1] * combs) % mod; } return dp[n]; } }; int main() { Solution obj; cout << obj.countOrders(2); }