An array arr consisting of n integers is given. The dominator of arr is the value that occurs in more than half of the elements of arr.

Write a function dominator(arr) that returns the dominator of arr. The function should return −1 if array does not have a dominator. All values in arr will be >=0.

For example, consider the array such that arr = [3,4,3,2,3,1,3,3]
The dominator of arr is 3 because it occurs in 5 out of 8 elements of arr and 5 is more than half of 8.
dominator([3,4,3,2,3,1,3,3]) => 3
dominator([1,2,3,4,5]) => -1

Tests:
dominator([3,4,3,2,3,1,3,3])
dominator([1,1,1,2,2,2]),
dominator([1,1,1,2,2,2,2])

Good luck!

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