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For a binary tree T, we can define a flip operation as follows: choose any node, and swap the left and right child subtrees. A binary tree X is flip e 阅读全文
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Given two sequences pushed and popped with distinct values, return true if and only if this could have been the result of a sequence of push and pop o 阅读全文
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Alice has a hand of cards, given as an array of integers. Now she wants to rearrange the cards into groups so that each group is size W, and consists 阅读全文
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You have a lock in front of you with 4 circular wheels. Each wheel has 10 slots: '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'. The wheels can rota 阅读全文
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Given a list of airline tickets represented by pairs of departure and arrival airports [from, to], reconstruct the itinerary in order. All of the tick 阅读全文
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Equations are given in the format A / B = k, where A and B are variables represented as strings, and k is a real number (floating point number). Given 阅读全文