Sort Each Adjacent Pair of an Array, Leaving an Odd Last Element in Place

Given an array of integers, sort it by pairs. Split the array into consecutive pairs starting from the first element, (nums[0], nums[1]), (nums[2], nums[3]), and so on, and put the two numbers of every pair in ascending order. Pairs never move relative to one another, and no number moves from one pair into another.

If the array has an odd length, the last number has no partner and stays where it is.

Function Signature

def sort_pairs(nums: list[int]) -> list[int]:

Rules

• For every even index i with i + 1 < len(nums), the output holds the smaller of nums[i] and nums[i + 1] at index i and the larger at index i + 1.
• If len(nums) is odd, the last element of the output equals the last element of nums.
• A pair of equal values is left as it is.
• Return a list of the same length as nums. You may reorder nums in place and return it, or return a new list.

Constraints

• 1 <= len(nums) <= 10^5
• -10^9 <= nums[i] <= 10^9

Examples

Example 1

Input: nums = [5, 4, 2, 3, 7]
Output: [4, 5, 2, 3, 7]

The pair (5, 4) becomes (4, 5), the pair (2, 3) is already in order, and 7 has no partner, so it does not move.

Example 2

Input: nums = [9, 1, 8, 2]
Output: [1, 9, 2, 8]

Each pair is sorted on its own. The result as a whole is not sorted, and it should not be.

Example 3

Input: nums = [6]
Output: [6]