Remove Duplicates

Time complexity - $O (n)$

class Solution:
 
    def removeDuplicates(self, nums: List[int]) -> int:
 
        k = 1
 
        for i in range(1, len(nums)):
 
            if nums[i] != nums[i-1]:
 
               nums[k] = nums[i]
 
               k += 1
 
        return k

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