Example - Remove Duplicates

Problem: Remove duplicates from sorted array in place.

function removeDuplicates(nums):
    if nums.length == 0: return 0
    write = 1
    for read from 1 to nums.length - 1:
        if nums[read] != nums[read-1]:
            nums[write] = nums[read]
            write++
    return write

Example: $[1,1,2,2,3]$ → $[1,2,3,...]$, length $3$.

Time: $O(n)$. Space: $O(1)$.