Catalan Number
Description
About Catalan Number here is the description
The array of the number is: 1, 1, 2, 5, 14, 42, 132, 429, 1430, 4862, 16796, 58786….
def catalan_number(n):
nm = dm = 1
for k in range(2, n+1):
nm, dm = ( nm*(n+k), dm*k )
return nm/dm
Leetcode Test
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Binary Search Tree
About how many structurally unique BST(binary search trees) that store value O(n)?