随笔分类 - LeetCode
摘要：Given an integer, write an algorithm to convert it to hexadecimal. For negative integer, two’s complement method is used. Note: Example 1: Example 2:
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摘要：Find the sum of all left leaves in a given binary tree. Example: 这道题让我们求一棵二叉树的所有左子叶的和，那么看到这道题我们知道这肯定是考二叉树的遍历问题，那么最简洁的写法肯定是用递归，由于我们只需要累加左子叶之和，那么我们在进入递归
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摘要：A binary watch has 4 LEDs on the top which represent the hours (0-11), and the 6 LEDs on the bottom represent the minutes (0-59). Each LED represents
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摘要：Given an integer n, return the nth digit of the infinite integer sequence [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, ...]. Example 1: Input: n = 3 Output: 3
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摘要：A frog is crossing a river. The river is divided into x units and at each unit there may or may not exist a stone. The frog can jump on a stone, but i
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摘要：Given a non-negative integer num represented as a string, remove k digits from the number so that the new number is the smallest possible. Note: The l
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摘要：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
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摘要：Given an array of integers with possible duplicates, randomly output the index of a given target number. You can assume that the given target number m
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摘要：Given a positive integer n and you can do operations as follow: What is the minimum number of replacements needed for n to become 1? Example 1: Exampl
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摘要：Given an array of integers A and let n to be its length. Assume Bk to be an array obtained by rotating the array A k positions clock-wise, we define a
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摘要：There is a list of sorted integers from 1 to n. Starting from left to right, remove the first number and every other number afterward until you reach
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摘要：Find the length of the longest substring T of a given string (consists of lowercase letters only) such that every character in T appears no less than
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摘要：Given an encoded string, return its decoded string. The encoding rule is: k[encoded_string], where the encoded_string inside the square brackets is be
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摘要：A character in UTF8 can be from 1 to 4 bytes long, subjected to the following rules: This is how the UTF-8 encoding would work: Given an array of inte
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摘要：Given a string s and a string t, check if s is subsequence of t. You may assume that there is only lower case English letters in both s and t. t is po
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摘要：Given N axis-aligned rectangles where N > 0, determine if they all together form an exact cover of a rectangular region. Each rectangle is represented
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摘要：Given two strings s and t which consist of only lowercase letters. String t is generated by random shuffling string s and then add one more letter at
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摘要：Suppose we abstract our file system by a string in the following manner: The string "dir\n\tsubdir1\n\tsubdir2\n\t\tfile.ext" represents: The director
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摘要：Given a string, find the first non-repeating character in it and return it's index. If it doesn't exist, return -1. Examples: Note: You may assume the
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摘要：Given an integer n, return 1 - n in lexicographical order. For example, given 13, return: [1,10,11,12,13,2,3,4,5,6,7,8,9]. Please optimize your algori
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