LeetCode - Unique Binary Search Trees

25 Jan 2018 • LeetCode(Second)

Question Definition

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

Java Solution

public int numTrees(int n) {
    int[] dp = new int[n + 1];
    dp[0] = 1;
    dp[1] = 1;
    for(int i = 2; i <= n; i++){
        for(int j = 1; j <= i; j++){
            dp[i] += dp[j - 1] * dp[i - j];
        }
    }
    return dp[n];
}

LeetCode(Second) Medium Dynamic Programming

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