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# Category Archives: 算法题

## Unique Binary Search Trees leetcode

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. 这道题目，乍一看很吓人，其实仔细分析，有如下规律：当我们在1-n中选择i作为根，其可能出现的情况为[1,i-1]中BST种类 和 [i+1,n]中BST种类的 乘积， 因此n个节点的总可能性就是把1到n逐步作为根节点的情况总数，而每一个情况又可以按照同样的方式继续计算，因此，我们可以将问题逐步缩小。tip：可以用DP讲计算过的结果存储起来。 Advertisements

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## Substring with Concatenation of All Words

You are given a string, S, and a list of words, L, that are all of the same length. Find all starting indices of substring(s) in S that is a concatenation of each word in L exactly once and without … Continue reading