#Leetcode# 96. Unique Binary Search Trees

Posted 2021-11-27 zlrrrr

https://leetcode.com/problems/unique-binary-search-trees/

 

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

Example:

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

代码：

class Solution {
public:
    int numTrees(int n) {
        vector<int> dp(n + 1, 0);
        dp[0] = 1;
        dp[1] = 1;
        for(int i = 2; i <= n; i ++) {
            for(int j = 0; j < i; j ++) 
                dp[i] += dp[j] * dp[i - j - 1];
        }
        return dp[n];
    }
};

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