How to Remove Duplicates In-Place From a Sorted Array in Python

Problem Description:

Given a sorted array, remove duplicate elements in‑place so that each element appears only once and return the new length of the array. The operation must use O(1) extra space.

Example

Example 1:

Input: nums = [1,1,2]

Output: 2, and the first two elements of nums become [1,2]. Elements beyond the new length can be ignored.

Example 2:

Input: nums = [0,0,1,1,1,2,2,3,3,4]

Output: 5, and the first five elements become [0,1,2,3,4].

Solution Idea

Iterate through the list and remove an element when it is equal to the next one.

Code

class Solution(object):
    def removeDuplicates(self, nums):
        """ 
        :type nums: List[int]
        :rtype: int
        """
        i = 0
        while ( i < len(nums) ):
            if i+2 <= len(nums):
                # the element at i+1 exists
                if nums[i] == nums[i+1]:
                    nums.remove(nums[i])
                    i -= 1
            else:
                return len(nums)
            i += 1