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All DNA is composed of a series of nucleotides abbreviated as A, C, G, and T, for example: "ACGAATTCCG". When studying DNA, it is sometimes useful to 阅读全文
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Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST. Calling next() will return the n 阅读全文
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Design and implement a TwoSum class. It should support the following operations: add and find. add - Add the number to an internal data structure.find 阅读全文
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Given an array of integers that is already sorted in ascending order, find two numbers such that they add up to a specific target number. The function 阅读全文
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Given a binary tree where all the right nodes are either leaf nodes with a sibling (a left node that shares the same parent node) or empty, flip it up 阅读全文
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Find the contiguous subarray within an array (containing at least one number) which has the largest product. For example, given the array [2,3,-2,4], 阅读全文
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Evaluate the value of an arithmetic expression in Reverse Polish Notation. Valid operators are +, -, *, /. Each operand may be an integer or another e 阅读全文