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Foreword
Over the last month found every day in the form of [a] series of questions and not appropriate to update the title, one is not enough to update the appropriate topic, and second, separate out is not a problem in terms of the system, it should be more a similar topic on talk together, so as to achieve the effect of giving top priority, so I decided to stop [a day] series title changed to [summary] week, then once a month and then monthly summary, then get down to business.
The first week of November a total of 20 questions, all the source code and the corresponding problem-solving ideas even open source to GitHub, a public reply No. "LeetCode" get with the following breakdown.
Mapping
Such common data structure Title: map, unordered_map, set or array using the hash mapping.
- 0242_valid_anagram
- 0290_word_pattern
- 0299_bulls_and_cows
more than three questions are dual mapping relationships between characters or strings is established, use the map according to the situation, unordered_map or can use an array - 0349_intersection_of_two_arrays
- 0350_intersection_of_two_arrays_ii
above two questions is to solve the intersection of two arrays, the first question only to find there are several different then, does not care about the number; the second topic need to find out the specific number of the same characters, also count duplicate - 0383_ransom_note
This topic is a query whether a string contains another string of characters not less than the number of
Depth-first search
- 0257_binary_tree_paths
Riddles
This topic is more interesting, just began to think of a variety of practices, but it feels too complicated, should time out, think Well, look at the official solution to a problem, the result was just a get, I ***, and analytical reading after only say, clothes, and interested can take a look at the official solution, not go into here.
- 0292_nim_game
mathematics
Such questions are the subject of mathematical methods can be used to solve, not much study data structures.
- 0258_add_digits
- 0263_ugly_number
- 0268_missing_number
该题目有多种解法，第一种是根据递增数组求解，然后计算差值就可得到确实的数是哪一个；第二种是官方给出的一种，通过异或运算得出，方法很有意思；两种方法复杂度相同 - 0303_range_sum_query_immutable
这个题目就是预先计算积分即可，了解图像处理的都知道图像积分这个概念，只不过这里是一维数组，而图像是二维的(不考虑颜色通道时)，所以很简单 - 0326_power_of_three
- 0342_power_of_four
这两个题目是判断给定数是否是某个数的幂，最简单的方法就是暴力分解，一种做法是将给定数转化成对应数的进制，即3进制或4进制，转换后的数如果是它的幂，那么一定只含有一个 1，所以判断一下就行了；另一种方法就是如果先找出最大的幂是多少，如果给定数也是，那么最大幂一定可以整除这个数，复杂度为O(1)
二分法
二分法就没什么好说的了，就那些操作，左右各一个，中间数大了右边的往左移动，中间数小了左边的往右移动，直到结束即可。
- 0278_first_bad_version
- 0367_valid_perfect_square
- 0374_guess_number_higher_or_lower
反转数组
反转数组就是使用双指针了，第一个题目直接进行即可，第二个题目只反转元音字母，所以指针移动时不再是++或--操作，而是以元音字母为单位移动，也没什么复杂的。
- 0344_reverse_string
- 0345_reverse_vowels_of_a_string
位运算
根据计算机原理，使用二进制的异或和与运算实现加法，其中异或表示加法，与运算表示进位。
- 0371_sum_of_two_integers