【LeetCode】96. 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

给定1...n数字序列,求共可以构造出多少不同的二叉树。

我们用数字i作为根节点,1....(i-1)就作为根节点左子树上的值,(i+1).....n就作为根节点右子树。

https://blog.csdn.net/u012501459/article/details/46622501

class Solution {
public:
    int numTrees(int n) {
        //递归求解
        // if(n==0||n==1)
        //     return 1;
        // int result = 0;
        // for(int i=0; i<n; i++){
        //     result += numTrees(i)*numTrees(n-i-1);
        // }
        // return result;
        
        //非递归
        int *G = new int[n+1]();
        G[0] = 1;
        G[1] = 1;
        for(int i=2; i<=n; i++){
            for(int j=0; j<i; j++){
                G[i] += G[j]*G[i-j-1];    
            }
            
        }
        return G[n];
    }
};


 

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转载自blog.csdn.net/poulang5786/article/details/81321456