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Given two integers n and k, return all possible combinations of k numbers out of 1 ... n. For example, If n = 4 and k = 2, a solution is: [ [2,4], [3, 阅读全文
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Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). For example, this binary tree [1,2,2,3,4,4,3] is symmet 阅读全文
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Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists. 思路： 由于链表 阅读全文
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Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST. 思路：利用快慢指针找到中间节点，作为根节点，然后左子树即为左边链表部分，右子树即 阅读全文
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We define the Perfect Number is a positive integer that is equal to the sum of all its positive divisors except itself. Now, given an integer n, write 阅读全文
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Given two strings representing two complex numbers. You need to return a string representing their multiplication. Note i2 = -1 according to the defin 阅读全文
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Given an array where elements are sorted in ascending order, convert it to a height balanced BST. 思路： 由于是有序数组，那么根节点肯定是中间的那个数字，然后递归处理左子树和右子树即可。 阅读全文
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Given a binary tree, find the maximum path sum. For this problem, a path is defined as any sequence of nodes from some starting node to any node in th 阅读全文
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Given a string, find the length of the longest substring without repeating characters. Examples: Given "abcabcbb", the answer is "abc", which the leng 阅读全文
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Implement pow(x, n). 开始的时候思路很朴素，隐约觉得不太对劲。。果然，超时了。 然后，再仔细琢磨，发现可以缩短时间，缩短到 O(lgn)的复杂度。 比如8个2相乘的话，可以表示为4的平方，4又可以表示为2的平方，只需三次即可算出。 参考： https://discuss.leet 阅读全文