Remove Duplicates from Sorted Array

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Given an integer array nums sorted in non-decreasing order, remove the duplicates in-place such that each unique element appears only once. The relative order of the elements should be kept the same. Then return the number of unique elements in nums.

Consider the number of unique elements of nums to be k, to get accepted, you need to do the following things:

• Change the array nums such that the first k elements of nums contain the unique elements in the order they were present in nums initially. The remaining elements of nums are not important as well as the size of nums.

• Return k.

Custom Judge:

The judge will test your solution with the following code:

int[] nums = [...]; // Input array
int[] expectedNums = [...]; // The expected answer with correct length

int k = removeDuplicates(nums); // Calls your implementation

assert k == expectedNums.length;
for (int i = 0; i < k; i++) {
    assert nums[i] == expectedNums[i];
}

If all assertions pass, then your solution will be accepted.

Example 1:

Input: nums = [1,1,2]
Output: 2, nums = [1,2,_]
Explanation: Your function should return k = 2, with the first two elements of nums being 1 and 2 respectively.
It does not matter what you leave beyond the returned k (hence they are underscores).

Example 2:

Input: nums = [0,0,1,1,1,2,2,3,3,4]
Output: 5, nums = [0,1,2,3,4,_,_,_,_,_]
Explanation: Your function should return k = 5, with the first five elements of nums being 0, 1, 2, 3, and 4 respectively.
It does not matter what you leave beyond the returned k (hence they are underscores).

Constraints:

• 1 <= nums.length <= 3 * 104

• -100 <= nums[i] <= 100

• nums is sorted in non-decreasing order.

You can solve this problem by using two pointers. Here's a JavaScript implementation:

function removeDuplicates(nums) {
    if (nums.length === 0) return 0;
    
    let uniqueIndex = 0;

    for (let i = 1; i < nums.length; i++) {
        if (nums[i] !== nums[uniqueIndex]) {
            uniqueIndex++;
            nums[uniqueIndex] = nums[i];
        }
    }

    return uniqueIndex + 1;
}

// Test cases
const nums1 = [1, 1, 2];
console.log(removeDuplicates(nums1)); // Output: 2, nums1 = [1, 2, _]

const nums2 = [0, 0, 1, 1, 1, 2, 2, 3, 3, 4];
console.log(removeDuplicates(nums2)); // Output: 5, nums2 = [0, 1, 2, 3, 4, _, _, _, _, _]

In this implementation, the removeDuplicates function iterates through the array using two pointers. The uniqueIndex pointer points to the last unique element found so far. If the current element is different from the element at the uniqueIndex, it increments uniqueIndex and updates nums[uniqueIndex] with the current element. Finally, it returns the number of unique elements found.