【LeetCode】96.Unique Binary Search Trees(Medium)解题报告

【LeetCode】96.Unique Binary Search Trees(Medium)解题报告

题目地址：https://leetcode.com/problems/unique-binary-search-trees/description/

题目描述：

  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

Solution:

/*
dp
f(n) = f(0)*f(n-1) + f(1)*f(n-2)+...
*/
class Solution {
public int numTrees(int n) {
int[] res = new int[n+1];
res[0]=1;
for(int i=1 ; i<=n ; i++){
for(int j=0 ; j<i ; j++){
res[i] += res[j] * res[i-j-1];
}
}
return res
;
}
}

Date：2018年3月29日