LeetCode——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

题目：给定n,有多少个1到n的二叉搜索树？

思路：问题可以分成两步，一是(1,i-1)的个数，一是(i+1,n)的个数，两者相乘，就是总的个数。

	public int numTrees(int n) {
		if(n == 1 || n == 0)
			return 1;
		else{
			int num = 0;
			for(int i=1;i<=n;i++)
				num += numTrees(i - 1) * numTrees(n - i);
			return num;
		}
	}

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LeetCode——Unique Binary Search Trees

原文：http://blog.csdn.net/laozhaokun/article/details/38347855