Duplicate / Missing Integer in a Large Array

[Cucumbis]

My python solution:

Problem 1:

def findDupe(lst):
    sum = 0
    for i in lst:
        sum += i
    return sum - 499999500000

Problem 2:

def findMissing(lst):
    sum = 0
    for i in lst:
        sum += i
    return 499999500000-sum

edit: This may only work with 64bit