Dominator

[acha-bill]

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

For example, consider array A such that

A = [3, 4, 2, 3, 2, 2, -1, 3, 3]

The dominator of A is 3 because it occurs in 5 out of 8 elements of A (namely in those with indices 0, 2, 4, 6 and 7) and 5 is more than a half of 8.

Write a function that, given an array, A consisting of N integers, returns the index of any element of array A in which the dominator of A occurs. The function should return −1 if array A does not have a dominator.

For example, given array A such that

 A[0] = 3    A[1] = 4    A[2] =  3
 A[3] = 2    A[4] = 3    A[5] = -1
 A[6] = 3    A[7] = 3

the function may return 0, 2, 4, 6 or 7, as explained above. (All those indexes are the indexes that holds 3)