I completed this challenge 28, but the code takes way too long to process with a range of a million digits from 1 to a million. If you limit either the amount of digits or the range pool then it runs quickly enough. fun times!

Challenge28.py

# The array duplicates problem is when one integer is in an array for more than once.
# If you are given an array with integers between 1 and 1,000,000 or in some other interval
# and one integer is in the array twice. How can you determine which one?
import random

print "Creating a list of random numbers from 1 to 1,000,000."
numSet = []
for i in range(1, 1000000):
    numSet.append(random.randint(1, 100))
checkList = []
checkDouble = []
for i in numSet:
    if i in checkList:
        if i in checkDouble:
            continue
        checkDouble.append(i)
        print "%d is located at these positions in the array:" % (i)
        for n in (n for n,x in enumerate(numSet) if x == i):
            print n
    else:
        checkList.append(i)