public class Solution { public int chordCnt(int n) { long mod = 1000000000 + 7; long dp[] = new long[n+1]; dp[0] = 1 ; dp[1] = 1; for(int k = 2 ; k <= n ; k++){ for(int i = 0 , j = k-1 ; i <= k-1 ; i++ , j--) dp[k]= (dp[k]%mod + (((dp[i]%mod)*(dp[j]%mod))%mod))%mod; } return (int)(dp[n] % mod); } }