unique_integer.py

# -*- coding: utf-8 -*-

from collections import Counter
from random import randint


def solution(A):
    unique_integers = [
        integer
        for integer, count in Counter(A).iteritems()
        if count == 1
    ]
    if unique_integers:
        for integer in A:
            if integer in unique_integers:
                return integer
    return -1

print solution([])
print solution([
    randint(1, 1000000000)
    for _ in xrange(0, 100000)
])