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"""
Testcases:
Input:
[]
[1,1,2]
[1,1,1]
[0]

Output:
[]
[1,2]
[1]
[0]

"""
class Solution(object):
    def removeDuplicates(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        
        
        if not nums:
            return 0;
            
        res = 0;  # res is used to maintain the n th element in nums without repetition
        # res starts from 0;
        
        for i in range(1,len(nums)):
            
            if nums[i] != nums[res]:
                res += 1;
                nums[res] = nums[i];
                
        return res + 1;

public class Solution {
    public int removeDuplicates(int[] nums) {
        int m = nums.length;
        int res = 0;
        for(int i = 1; i < m; i++){
            if(nums[i] != nums[res]){
                nums[++res] = nums[i];
            }
            
        }
        return res + 1;
    }
}