LeetCode 96. Unique Binary Search Trees

发表于 更新于 分类于 本文字数： 544 阅读时长 ≈ 1 分钟
LeetCode 96. Unique Binary Search Trees

96. Unique Binary Search Trees

Difficulty:: Medium

Given n, how many structurally unique BST’s (binary search trees) that store values 1 … n?

Example:

1
2
3
4
5
6
7
8
9
10
11
Input: 3
Output: 5
Explanation:
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

Solution

Language: Java

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
class Solution {
    public int numTrees(int n) {
        if (n == 0) {
            return 0;
        }
        if (n == 1) {
            return 1;
        }
        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];
        
    }
}