#Leetcode# 96. Unique Binary Search Trees

发布时间：2020-12-14 04:31:39 所属栏目：大数据来源：网络整理

导读：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: 3Output: 5Explanation:Given n = 3,there are a total of 5 unique BS

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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