java Remove Duplicate Elements from Sorted Array

Description of the problem

Given a sorted array, remove the repeated elements from the array, keep only one repeated element, and return the new array length.

Requirements:
Do not allocate extra space for the array, you must use constant memory size for in-place operations.

For example:
Given the sorted array A=[1,1,2], and your function must return the length length=2, and A is now changed to [1,2].

Input

An already sorted array, for example, [1,1,2].

Output

Return the new length of the array, for example, length=2.

Two-pointer method

Set the fast pointer to traverse the array and the slow pointer to point to the next element of the non-repeated element.

public static int removeDuplicates(int[] nums)
{
  if (nums.length < 1)
    return nums.length;
  int slow = 1;
  for (int fast = 1; fast < nums.length; fast++) {
    if (nums[fast] != nums[slow - 1]) {
      nums[slow++] = nums[fast];
    }
  }
  return slow;
}

Animation demonstration:

Expansion

Remove duplicate elements from the sorted array and retain the specified number of digits.

public static int removeDuplicatesN(int[] nums, int repeatN)
{
 if (nums.length <= repeatN)
  return nums.length;
 int index = repeatN;
 for (int i = repeatN; i < nums.length; i++) {
  if (nums[i] != nums[index - repeatN]) {
   nums[index++] = nums[i];
  }
 }
 return index;
}

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