Remove Duplicates from Sorted Array in Java

Remove Duplicates from Sorted Array in Java

This guide explains the intuition, optimized approach, and Java implementation for remove duplicates from sorted array in java, with practical tips for interviews and production coding standards.

Problem

Remove duplicates from sorted array in-place and return count of unique elements.

Two Pointer Strategy

• slow tracks last unique index
• fast scans array
• when new value found, write at slow + 1

Java Solution

class Solution {
    public int removeDuplicates(int[] nums) {
        if (nums.length == 0) return 0;

        int slow = 0;
        for (int fast = 1; fast < nums.length; fast++) {
            if (nums[fast] != nums[slow]) {
                slow++;
                nums[slow] = nums[fast];
            }
        }

        return slow + 1;
    }
}

Complexity

• Time: O(n)
• Space: O(1)

Key Takeaways

• Start from the brute-force idea, then derive the optimized invariant.
• Use clean pointer/index boundaries to avoid off-by-one bugs.
• Validate against edge cases (empty input, single element, duplicates, extreme values).