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Given a string S and a string T, find the minimum window in S which will contain all the characters in T in complexity O(n). Example: Input: S = "ADOB 阅读全文
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Remove the minimum number of invalid parentheses in order to make the input string valid. Return all possible results. Note: The input string may cont 阅读全文
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Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses. For example, given n = 3, a solution set is: [ 阅读全文
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Write a function to generate the generalized abbreviations of a word. Note: The order of the output does not matter. Example: Input: "word" Output: [" 阅读全文
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Given a string that contains only digits 0-9 and a target value, return all possibilities to add binary operators (not unary) +, -, or * between the d 阅读全文
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You are given a list of non-negative integers, a1, a2, ..., an, and a target, S. Now you have 2 symbols + and -. For each integer, you should choose o 阅读全文
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A strobogrammatic number is a number that looks the same when rotated 180 degrees (looked at upside down). Find all strobogrammatic numbers that are o 阅读全文
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Given a string containing only digits, restore it by returning all possible valid IP address combinations. A valid IP address consists of exactly four 阅读全文
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所谓优化剪枝策略，就是判断当前的分支树是否符合问题的条件，如果当前分支树不符合条件，那么就不再遍历这个分支里的所有路径。回溯算法使用剪枝函数，剪去一些不可能到达 最终状态（即答案状态）的节点，从而减少状态空间树节点的生成。 有个解空间，要从里面挑。有条件，不符合就剪枝：一般是数组长度够了就行了可是一 阅读全文
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Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. A mapping of digit to le 阅读全文