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Huahua's Tech Road

花花酱 LeetCode 451. Sort Characters By Frequency

Given a string, sort it in decreasing order based on the frequency of characters.

Example 1:

Example 2:

Example 3:



花花酱 LeetCode 520. Detect Capital

Given a word, you need to judge whether the usage of capitals in it is right or not.

We define the usage of capitals in a word to be right when one of the following cases holds:

  1. All letters in this word are capitals, like “USA”.
  2. All letters in this word are not capitals, like “leetcode”.
  3. Only the first letter in this word is capital if it has more than one letter, like “Google”.

Otherwise, we define that this word doesn’t use capitals in a right way.

Example 1:

Example 2:

Note: The input will be a non-empty word consisting of uppercase and lowercase latin letters.


花花酱 LeetCode 422. Find All Duplicates in an Array

Given an array of integers, 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.

Find all the elements that appear twice in this array.

Could you do it without extra space and in O(n) runtime?



花花酱 LeetCode 128. Longest Consecutive Sequence

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

For example,
Given [100, 4, 200, 1, 3, 2],
The longest consecutive elements sequence is [1, 2, 3, 4]. Return its length: 4.

Your algorithm should run in O(n) complexity.


花花酱 Leetcode 371. Sum of Two Integers

Calculate the sum of two integers a and b, but you are not allowed to use the operator + and -.