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Given n, how many structurally unique BST's (binary search trees) that store values 1 ... n? Example: Approach #1: DP. [C++] Analysis: status: nums[n] 阅读全文
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Additive number is a string whose digits can form additive sequence. A valid additive sequence should contain at least three numbers. Except for the f 阅读全文
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On a 2-dimensional grid, there are 4 types of squares: 1 represents the starting square. There is exactly one starting square. 2 represents the ending 阅读全文
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Given a string S, we can transform every letter individually to be lowercase or uppercase to create another string. Return a list of all possible stri 阅读全文
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We are given N different types of stickers. Each sticker has a lowercase English word on it. You would like to spell out the given target string by cu 阅读全文
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Suppose you have N integers from 1 to N. We define a beautiful arrangement as an array that is constructed by these N numbers successfully if one of t 阅读全文
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A binary watch has 4 LEDs on the top which represent the hours (0-11), and the 6 LEDs on the bottom represent the minutes (0-59). Each LED represents 阅读全文
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Given a non-negative integer n, count all numbers with unique digits, x, where 0 ≤ x < 10n. Example: Input: 2 Output: 91 Explanation: The answer shoul 阅读全文
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Given a string s, partition s such that every substring of the partition is a palindrome. Return all possible palindrome partitioning of s. Example: I 阅读全文
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Given a non-empty string s and a dictionary wordDict containing a list of non-empty words, add spaces in s to construct a sentence where each word is 阅读全文