Thinking process

return number of possible BST structure, try to find the pattern

can I get 3 from 2?

public class Solution {
    public int numTrees(int n) {
        if (n <= 2) return n;

        int[] dp = new int[n + 1];
        dp[0] = 1;
        dp[1] = 1;
        dp[2] = 2;

        for (int i = 3; i <= n; ++i) {
            for (int j = 1; j <= i; ++j) {
                dp[i] = dp[i] + dp[j - 1] * dp[i - j];
            }
        }

        return dp[n];
    }
}

Follow up - Given in-oreder traversal result of Binary tree

same as above