Find All Duplicates in an Array

You must write an algorithm that runs in O(n) time and uses only constant extra space.

-> No hashmap ..

Solution Idx	Time Complexity	Space Complexity	Comment
1	O(n^2)	O(1)	Two Pointer Scanning
2	O(n)	O(n)	Hashmap detector
3	O(nlogn)	O(1)	Sort and check duplicate
4	O(n)	O(1)	Using nums as frequency container using minus operator