Remove Duplicates from Sorted Array

Easy

Given a sorted array nums, remove the duplicates in-place such that each unique element appears only once. Return the number of unique elements. The relative order of elements should be kept the same.

Examples

Input	Output
nums = [1,1,2]	2, nums = [1,2,_]
nums = [0,0,1,1,1,2,2,3,3,4]	5, nums = [0,1,2,3,4,_,_,_,_,_]

Python Solution

def remove_duplicates(nums: list[int]) -> int:
    if not nums:
        return 0
    write = 1
    for read in range(1, len(nums)):
        if nums[read] != nums[read - 1]:
            nums[write] = nums[read]
            write += 1
    return write

JavaScript Solution

function removeDuplicates(nums) {
  if (!nums.length) return 0;
  let write = 1;
  for (let read = 1; read < nums.length; read++) {
    if (nums[read] !== nums[read - 1]) {
      nums[write++] = nums[read];
    }
  }
  return write;
}

Step-by-Step Explanation

Use two pointers: read scans the array, write is where we place the next unique element.
When we see a new value (different from previous), copy it to write and increment write.
Return write as the count of unique elements.

Complexity Analysis

Time	O(n)
Space	O(1)

Related Tools

JSON Formatter

All Problems

Two Sum Reverse a String Palindrome Check FizzBuzz Binary Search Reverse Linked List Merge Two Sorted Arrays Valid Parentheses Maximum Subarray (Kadane's Algorithm)Nth Fibonacci Number Valid Anagram First Unique Character Climbing Stairs Roman to Integer Best Time to Buy and Sell Stock Contains Duplicate Move Zeroes Intersection of Two Arrays Longest Common Prefix