SingleNumber.py

'''
Given an array of integers, 
every element appears twice except for one. 
Find that single one.
Your algorithm should have a linear runtime complexity.
Could you implement it without using extra memory?
'''
'''
find the single occurence number in array of integers whose occurence are two 
except one
args: array of integers
return: the once occurence number in the array
'''
def single_num(arr):
 # create a map for the occurence of number
 map = {}
 for num in arr:
 if num in map:
 map[str(num)] += 1
 else:
 map[str(num)] = 1
 # look for the num
 for key in map:
 if map[key] == 1:
 return key
 else:
 return None

test = [1,2,2,4,4]
print single_num(test)


'''
Given an array of integers, 
every element appears three times except for one. 
Find that single one.

Note:
Your algorithm should have a linear runtime complexity. 
Could you implement it without using extra memory?

'''