leetcodeOJ 96. 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

参考代码：http://blog.csdn.net/linhuanmars/article/details/24761459

注意在C、C++中，声明数组

int* ans = new int[n+1];ans[0] = 1;

属于undefined behavior。

代码如下：

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