Practice/Meta/Leetcode 26. Remove Duplicates from Sorted Array

Leetcode 26. Remove Duplicates from Sorted Array

CodingMust

Problem

You are given an integer array sorted in non-decreasing order. Your task is to modify the array in-place by moving all unique elements to the front of the array, preserving their relative order. After this operation, return the count of unique elements.

The array should be modified such that the first k positions contain each unique element exactly once in sorted order, where k is the number of distinct values. The contents of the array beyond position k do not matter.

You must accomplish this using only constant extra space (in-place modification).

Requirements

1. Modify the input array in-place to place unique elements at the beginning
2. Return an integer k representing the count of unique elements
3. The first k positions of the array must contain each unique element exactly once in sorted order
4. Use only O(1) extra space (no additional arrays or data structures proportional to input size)
5. Preserve the sorted order of unique elements

Constraints

• 1 ≤ nums.length ≤ 30,000
• -100 ≤ nums[i] ≤ 100
• The array is sorted in non-decreasing order

Examples

Example 1:

Input: nums = [1, 1, 2, 2, 3, 4, 4, 5] Output: 5 Explanation: After modification, nums = [1, 2, 3, 4, 5, _, _, _] where _ represents don't-care values. The function returns 5.

Example 2:

Input: nums = [7, 7, 7, 7] Output: 1 Explanation: Only one unique element exists. After modification, nums = [7, _, _, _] and the function returns 1.

Example 3:

Input: nums = [1, 2, 3, 4, 5] Output: 5 Explanation: All elements are already unique. The array remains unchanged and the function returns 5.