Introduction

In this blog post, we will explore how to solve the LeetCode problem "448" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

Given an array nums of n integers where nums[i] is in the range [1, n], return an array of all the integers in the range [1, n] that do not appear in nums. Example 1: Input: nums = [4,3,2,7,8,2,3,1] Output: [5,6] Example 2: Input: nums = [1,1] Output: [2] Constraints: n == nums.length 1 <= n <= 105 1 <= nums[i] <= n Follow up: Could you do it without extra space and in O(n) runtime? You may assume the returned list does not count as extra space.

Explanation

Here's the breakdown of the approach, complexities, and Python code:

• In-place Modification: The core idea is to utilize the input array nums itself as a hash table. We iterate through the array. For each number num, we find its corresponding index (num - 1). We then negate the value at that index if it's positive. This marks the presence of the number num in the array.

• Identifying Missing Numbers: After marking all present numbers by negating the values at corresponding indices, we iterate through the modified array. Any index i with a positive value indicates that the number i + 1 is missing from the original array.

• Returning the Result: We collect the missing numbers (i + 1) into a result list and return it.

• Complexity: O(n) time complexity and O(1) extra space complexity (excluding the output list, as specified in the problem).

Code

    def findDisappearedNumbers(nums):
    """
    Finds all numbers that are missing from the range [1, n] in an array of n integers.

    Args:
        nums: A list of integers where nums[i] is in the range [1, n].

    Returns:
        A list of all integers in the range [1, n] that do not appear in nums.
    """
    n = len(nums)
    for num in nums:
        index = abs(num) - 1
        if nums[index] > 0:
            nums[index] *= -1

    result = []
    for i in range(n):
        if nums[i] > 0:
            result.append(i + 1)

    return result