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25. Reverse Nodes in k-Group Given a linked list, reverse the nodes of a linked list k at a time and return its modified list. k is a positive integer 阅读全文
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24. Swap Nodes in Pairs Given a linked list, swap every two adjacent nodes and return its head. You may not modify the values in the list's nodes, onl 阅读全文
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23. Merge k Sorted Lists Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity. Example: 阅读全文
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22. Generate Parentheses Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses. For example, given n 阅读全文
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21. Merge Two Sorted Lists Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of th 阅读全文
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20. Valid Parentheses Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid. An input 阅读全文
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19. Remove Nth Node From End of List Given a linked list, remove the n-th node from the end of list and return its head. Example: 阅读全文
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18. 4Sum Given an array nums of n integers and an integer target, are there elements a, b, c, and d in nums such that a + b + c + d = target? Find all 阅读全文