Given a sorted integer array arr in non-decreasing order, modify arr in-place so that each unique element appears only once and the relative order is preserved. Return the number of unique elements, n_unique. The first n_unique elements of arr must contain the unique values in sorted order. Elements beyond index n_unique - 1 can be ignored.
Example 1
Input: [2,2,3,3,5,5,5,7]
Output: 4
Explanation: Unique values are [2,3,5,7], so n_unique = 4. arr[:4] should be [2,3,5,7].
Example 2
Input: [-3,-3,-2,-1,-1,0,0,1]
Output: 5
Explanation: Unique values are [-3,-2,-1,0,1], so n_unique = 5. arr[:5] should be [-3,-2,-1,0,1].
Constraints
Case 1
Input: [1,1,1,1,1]
Expected: 1
Case 2
Input: [4,5,6,7,8]
Expected: 5
Case 3
Input: [-10,-10,-10,-9,-8,-8,-7]
Expected: 4
Case 4
Input: [0,1,2,3,4,5,6,7,8,9]
Expected: 10
Case 5
Input: [-2,-2,-2,-2,-2,-2,-2,-2,-2,-2]
Expected: 1