Datastructure
Hashing
1) Find top three repeated in array(https://www.geeksforgeeks.org/find-top-three-repeated-array/)
Must read knapsack
https://www.quora.com/0-1-Integer-Knapsack-problem-without-items-repeating-How-do-I-approach
https://www.codesdope.com/course/algorithms-knapsack-problem/