Check Element Frequencies Evenness in Python

Suppose we have a list of elements called nums, we have to check whether all numbers appear even times or not. We have to solve it using constant space.

So, if the input is like nums = [8, 9, 9, 8, 5, 5], then the output will be True, because all number have occurred twice.

To solve this, we will follow these steps −

• if size of nums is odd, then

  • return False

• sort the list nums

• for i in range 1 to size of nums, do

  • if nums[i] is same as nums[i - 1], then

    • nums[i] := 0,

    • nums[i - 1] := 0

• return true when sum of all elements present in nums is same as 0 otherwise false

Example

Let us see the following implementation to get better understanding

def solve(nums):
   if len(nums) & 1:
      return False
   nums.sort()
   for i in range(1, len(nums)):
      if nums[i] == nums[i - 1]:
         nums[i] = nums[i - 1] = 0
   return sum(nums) == 0

nums = [8, 9, 9, 8, 5, 5]
print(solve(nums))

Input

[8, 9, 9, 8, 5, 5]

Output

True