# A zero-indexed 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[0] = 3    A[1] = 4    A[2] =  3
# A[3] = 2    A[4] = 3    A[5] = -1
# A[6] = 3    A[7] = 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
# def solution(A)
# that, given a zero-indexed array A consisting of N integers, returns 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.
# Assume that:
# N is an integer within the range [0..100,000];
# each element of array A is an integer within the range [−2,147,483,648..2,147,483,647].
# 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.
# Complexity:
# expected worst-case time complexity is O(N);
# expected worst-case space complexity is O(1), beyond input storage (not counting the storage required for input arguments).
# Result 100%, O(N) or O(NlogN) , submitted once

def solution(A):
    # write your code in Python 2.7
    N = len(A)
    stack = []
    count = 0
    candidate = -1
    for i in A:
        if len(stack) == 0:
            stack.append(i)
        else:
            if i == stack[-1]:
                stack.append(i)
            else:
                stack.pop()
    if len(stack) != 0:
        candidate = stack[-1]
    else:
        return candidate
    
    for k in A:
        if k == candidate:
            count += 1
        else:
            pass
    print "candidate = " , candidate
    if count > N//2 :
        return A.index(candidate)
    else:
        return -1
        
