https://leetcode.com/problems/top-k-frequent-elements/

Given a non-empty array of integers, return the k most frequent elements.

Example 1:

Input: nums = [1,1,1,2,2,3], k = 2
Output: [1,2]

Input: nums = [1], k = 1
Output: [1]

https://leetcode.com/problems/find-median-from-data-stream/

Median is the middle value in an ordered integer list. If the size of the list is even, there is no middle value. So the median is the mean of the two middle value.

For example,

[2,3,4], the median is 3

[2,3], the median is (2 + 3) / 2 = 2.5

Design a data structure that supports the following two operations:

• void addNum(int num) - Add a integer number from the data stream to the data structure.
• double findMedian() - Return the median of all elements so far.

Example:

addNum(1)
addNum(2)
findMedian() -> 1.5
addNum(3) 
findMedian() -> 2

https://leetcode.com/problems/find-k-pairs-with-smallest-sums/

You are given two integer arrays nums1 and nums2 sorted in ascending order and an integer k.

Define a pair (u,v) which consists of one element from the first array and one element from the second array.

Find the k pairs (u₁,v₁),(u₂,v₂) ...(u_k,v_k) with the smallest sums.

Example 1:

Input: nums1 = [1,7,11], nums2 = [2,4,6], k = 3
Output: [[1,2],[1,4],[1,6]] 
Explanation: The first 3 pairs are returned from the sequence: 
             [1,2],[1,4],[1,6],[7,2],[7,4],[11,2],[7,6],[11,4],[11,6]

Given a list of nail polishes and some collected posted repo on Instagram, you need to find the top words.

nail polish = ["OPI", "ColorClub", "CirqueColor", "DanceLegend", "Masura"]

repo = [

"OPI Original Nail Envy is a nail strengthener with wheat protein",

"ColorClub is a spa brand that is loved for it's great value and bright colors",

"As a top choice for professionals ColorClub is often featured in Nails Magazine.",

"Create amazingly transformed, and unique,  nails with DanceLegend spot-inducing blue top coat! DanceLegend Aquele importado top! "

"Um esmalte holográfico que vale a pena repetir vou reproduzir uma nail art do ano passado e por isso passei ele novamente ColorClub don’t harp on it"

"Booom diaaa! DanceLegend E voltando a programação normal do blog, temos um importadinho na área!"

]

Result: ["colorclub",  "dancelegend"]

https://leetcode.com/problems/the-k-weakest-rows-in-a-matrix/

Given a m * n matrix mat of ones (representing soldiers) and zeros (representing civilians), return the indexes of the k weakest rows in the matrix ordered from the weakest to the strongest.

A row i is weaker than row j, if the number of soldiers in row i is less than the number of soldiers in row j, or they have the same number of soldiers but i is less than j. Soldiers are always stand in the frontier of a row, that is, always ones may appear first and then zeros.

Example 1:

Input: mat = 
[[1,1,0,0,0],
 [1,1,1,1,0],
 [1,0,0,0,0],
 [1,1,0,0,0],
 [1,1,1,1,1]], 
k = 3
Output: [2,0,3]
Explanation: 
The number of soldiers for each row is: 
row 0 -> 2 
row 1 -> 4 
row 2 -> 1 
row 3 -> 2 
row 4 -> 5 
Rows ordered from the weakest to the strongest are [2,0,3,1,4]