Write a program to find 100 largest numbers out of an array of 1 billion numbers

Question

I recently attended an interview where I was asked \"write a program to find 100 largest numbers out of an array of 1 billion numbers.\"

I was only able to give a br

Answer 1

Two options:

(1) Heap (priorityQueue)

Maintain a min-heap with size of 100. Traverse the array. Once the element is smaller than first element in heap, replace it.

InSERT ELEMENT INTO HEAP: O（log100）
compare the first element: O(1)
There are n elements in the array, so the total would be O(nlog100), which is O(n)

(2) Map-reduce model.

This is very similar to word count example in hadoop. Map job: count every element's frequency or times appeared. Reduce: Get top K element.

Usually, I would give the recruiter two answers. Give them whatever they like. Of course, map reduce coding would be labor-some because you have to know every exact parameters. No harm to practice it. Good Luck.