LeetCode 96. Unique Binary Search Trees

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

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

Thought:

For bst of 1...n, it can be structured bu root i and left tree 1...i and right tree i+1....n, so dp is available

Code C++:

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

LeetCode 96. Unique Binary Search Trees

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原文地址：http://www.cnblogs.com/gavinxing/p/5685379.html