gistfile1.py

def arr_leader(values):
    storage = {}
    max_sum_key = values[0]
    max_sum_val = 1 
        
    for i in values:
        if storage.get(i) is None:
            storage[i] = 0 
        storage[i] += 1
        # stores the current highest sum
        if storage[i] > max_sum_val:
            max_sum_key = i 
            max_sum_val = storage[i]

    if max_sum_val > len(values) / 2:
        return max_sum_key
    return -1


if __name__ == '__main__':
    print arr_leader([1, 2, 3 , 5, 6 ,7, 3, 3 ,3 , 3, 3 ,3 ,3 ,3 ])
    print arr_leader([1, 2, 3 ,4 ])


#############################

> python2.6 ten_minutes.py 
3
-1