The challenge
Given a non-empty array of integers, every element appears twice except for one. Find that single one.
Note:
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?
Example 1:
Input: [2,2,1] Output: 1
Example 2:
Input: [4,1,2,1,2] Output: 4
The solution in Python
def singleNumber(nums):
# create a dictionary/hashmap
found = {}
# loop through the nums
for i in nums:
# add to map if not found
if i not in found:
found[i] = i
else:
# otherwise remove it
del found[i]
# loop through the found map and return the first item
for i in found:
return i