Compress Consecutive Integer Ranges

Compress Consecutive Integer Ranges

Given an unsorted list of integers nums, compress the values into a canonical comma-separated string of maximal consecutive ranges.

Rules

1. The output must be sorted in ascending order.
2. Duplicate values should be ignored.
3. If a number does not have an adjacent consecutive neighbor, represent it as a single integer (e.g., "5").
4. If two or more integers form a contiguous sequence [a, a+1, ..., b], represent the sequence as "a-b".

Function Signature

def compress_ranges(nums: list[int]) -> str:
    pass

Input and Output Format

• Input: A list of integers nums.
• Output: A single string with compressed ranges separated by commas, with no spaces.

Constraints

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

Examples

Example 1:

Input: nums = [1, 4, 5, 2, 3, 9, 8, 11]
Output: "1-5,8-9,11"
Explanation:
After sorting and removing duplicates, the numbers are [1, 2, 3, 4, 5, 8, 9, 11].
- 1 through 5 form a contiguous range: "1-5"
- 8 and 9 form a contiguous range: "8-9"
- 11 is standalone: "11"
Joined by commas: "1-5,8-9,11"

Example 2:

Input: nums = [3, 3, 3]
Output: "3"
Explanation: Duplicates are removed, leaving only the single value 3.

Example 3:

Input: nums = []
Output: ""
Explanation: An empty input produces an empty string.

Edge Cases to Consider

• Empty input array.
• Single element array.
• Arrays with negative numbers and sequences spanning across zero (e.g., [-2, -1, 0, 1]).
• Arrays consisting entirely of duplicate values.