LeetCode *** 96. Unique Binary Search Trees

题目：

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

分析：

找规律。

代码：

class Solution {
public:
int numTrees(int n) {

if (n == 0)return 0;

int *res = new int[n + 1];

res[0] = 1;
res[1] = 1;

for (int i = 2; i <= n; ++i) {
res[i] = 0;
for (int j = i; j>0; --j) {

res[i] += res[i - j] * res[j - 1];

}
}

return res
;
}
};