26. Remove Duplicates from Sorted Array

Intitution

In a sorted array, duplicates are always next to each other. So use a slow and fast pointer where the slow only moves when an unique element is encountered. Just scan through the array, and whenever we see a new (unique) element, overwrite the front part of the array with it, maintaining only the distinct values in-place.

Complexity

Space Complexity	Time Complexity
$\text{O}(1)$	$\text{O}(n)$

Code

public int removeDuplicates(int[] nums) {
    int i = 0, j = 0;

    // Traverse the array
    for(; i < nums.length;) {
        // If first element or current is not equal to the previous (i.e., it's unique)
        if(i == 0 || nums[i-1] != nums[i]) {
            nums[j] = nums[i];  // Place the unique element at the next available position
            j++;                // Move the insert pointer
        }
        i++; // Move to the next element
    }

    return j; // j is the new length of the array with unique elements
}