Given n, how many structurally unique BST's (binary search trees) that store values 1...n?
For example,
Given n = 3, there are a total of 5 unique BST's.
1 3 3 2 1 \ / / / \ \ 3 2 1 1 3 2 / / \ \ 2 1 2 3
class Solution { public: int numTrees(int n) { if(n <= 1) return 1; int ret = 0; for(int i = 0; i < n; ++i) { ret += numTrees(i) * numTrees(n-i-1); } return ret; } };
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