Remove Duplicates from Sorted Array

Maintain a unique prefix

For nonempty sorted input, set write = 1. Scan read from one onward; whenever nums[read] != nums[write - 1], assign it to nums[write] and increment write. The invariant is that nums[0..write-1] contains exactly the distinct values from the processed prefix in sorted order. Return write; values after it are irrelevant under the standard API. This uses O(n) time and O(1) extra space. Test empty input, one element, all equal values, no duplicates, and duplicate runs at either end. Do not allocate a set when the sorted contract permits compaction, and do not claim the whole original-length array has been physically shortened.