Day 31

Unique Binary Search Trees

The number of left subtrees is j - 1 and the number of right subtrees is i - j.

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class Solution {
    public int numTrees(int n) {
        int[] dp = new int[n + 1];
        dp[0] = 1;
        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= i; j++) {
                dp[i] += dp[j - 1] * dp[i - j];
            }
        }
        return dp[n];
    }
}
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func numTrees(n int) int {
	dp := make([]int, n+1)
	dp[0] = 1
	for i := 1; i <= n; i++ {
		for j := 1; j <= i; j++ {
			dp[i] += dp[j-1] * dp[i-j]
		}
	}
	return dp[n]
}