Solution to Single Number Problem

Single number problem

#Linear solution O(n)
#Constant space

def uniqueNumber(sequence) -> int:
    # flags which stores repeated numbers
    # It works for 3 repetions only
    once = 0
    twice = 0
    
    for num in sequence:
        once, twice = canBeSettedInFlag(num,once,twice)
        twice, once = canBeSettedInFlag(num,twice,once)
    return once

# Checks whether e (element) is already on destinationFlag, case not it will try set
# Before set in destinationFlag it validates whether another flag contains it, case not it will be setted
def canBeSettedInFlag(e, destinationFlag, otherFlag):
    destinationFlag = (destinationFlag ^ e) & ~ otherFlag
    return destinationFlag, otherFlag
    

sequence = [2,1,1,1,2,2,3]
print(uniqueNumber(sequence))