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Return the lexicographically smallest subsequence of s that contains all the distinct characters of s exactly once. Note: This question is the same as 阅读全文
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Given the root of a binary tree, consider all root to leaf paths: paths from the root to any leaf. (A leaf is a node with no children.) A node is insu 阅读全文
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You have n tiles, where each tile has one letter tiles[i] printed on it. Return the number of possible non-empty sequences of letters you can make usi 阅读全文
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Given words first and second, consider occurrences in some text of the form "first second third", where second comes immediately after first, and thir 阅读全文
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Given a matrix and a target, return the number of non-empty submatrices that sum to target. A submatrix x1, y1, x2, y2 is the set of all cells matrix[ 阅读全文
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Given two numbers arr1 and arr2 in base -2, return the result of adding them together. Each number is given in array format: as an array of 0s and 1s, 阅读全文
