Swap Even Index and Odd Index Elements in Python

Suppose we have a list of numbers called nums, we will exchange each consecutive even indexes with each other, and also exchange each consecutive odd index with each other.

So, if the input is like [1,2,3,4,5,6,7,8,9], then the output will be [3, 4, 1, 2, 7, 8, 5, 6, 9]

To solve this, we will follow these steps −

• length := size of nums
• for i in range 0 to length, increase by 4, do
  • if i+2<length, then
    • exchange nums[i] and nums[i+2]
  • if i+3<length, then
    • exchange nums[i+1] and nums[i+3]
• return nums

Let us see the following implementation to get better understanding −

Example

 Live Demo

class Solution:
   def solve(self, nums):
      length = len(nums)
      for i in range(0,length,4):
         if(i+2<length):
            nums[i], nums[i+2] = nums[i+2], nums[i]
         if(i+3<length):
            nums[i+1], nums[i+3] = nums[i+3], nums[i+1]
      return nums
ob = Solution()
nums = [1,2,3,4,5,6,7,8,9]
print(ob.solve(nums))

Input

[1,2,3,4,5,6,7,8,9]

Output

[3, 4, 1, 2, 7, 8, 5, 6, 9]