python_dominator_codility.py

from collections import defaultdict
from operator import itemgetter


def solution(A):
    # write your code in Python 2.7

    appearances = defaultdict(int)
    N=len(A)
    for each_key in A:
        appearances[each_key] += 1
    if not appearances:
        return -1
    max_elem=max(appearances.iteritems(), key=itemgetter(1))
    if max_elem[1]>(N/2):
        for k,v in enumerate(A):
            if v==max_elem[0]:
                return k
    else:
        return -1
        
if __name__ == '__main__':
    print 'Start tests..'
    assert solution(A) in [0, 2, 4, 6, 7]
    assert solution([2,1,3,1,4,1,5,1])==-1
    assert solution([]) == -1

    print 'Ok!'