Given an array of integers arr, randomly return an index of the maximum value seen by far.

Example:
Input: [11, 30, 2, 30, 30, 30, 6, 2, 62, 62]

Having iterated up to the at element index 5 (where the last 30 is), randomly give an index among [1, 3, 4, 5] which are indices of 30 - the max value by far. Each index should have a ¼ chance to get picked.

Having iterated through the entire array, randomly give an index between 8 and 9 which are indices of the max value 62.