Introduction

In this blog post, we will explore how to solve the LeetCode problem "581" 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 integer array nums, you need to find one continuous subarray such that if you only sort this subarray in non-decreasing order, then the whole array will be sorted in non-decreasing order. Return the shortest such subarray and output its length. Example 1: Input: nums = [2,6,4,8,10,9,15] Output: 5 Explanation: You need to sort [6, 4, 8, 10, 9] in ascending order to make the whole array sorted in ascending order. Example 2: Input: nums = [1,2,3,4] Output: 0 Example 3: Input: nums = [1] Output: 0 Constraints: 1 <= nums.length <= 104 -105 <= nums[i] <= 105 Follow up: Can you solve it in O(n) time complexity?

Explanation

Here's an efficient solution to find the shortest unsorted continuous subarray, along with an explanation:

• Identify the Boundaries: The core idea is to find the leftmost and rightmost elements that are out of order. These elements define the boundaries of the subarray that needs to be sorted.
• Finding the Minimum and Maximum Out-of-Order Elements: Scan from left to right to find the rightmost out-of-order element (end index). Simultaneously, scan from right to left to find the leftmost out-of-order element (start index). Then, identify the minimum and maximum values within this potential unsorted subarray.

• Extend Boundaries: Finally, extend the boundaries further. The start index should move to the left until we find an element smaller than the minimum out-of-order value. Similarly, the end index should move to the right until we find an element greater than the maximum out-of-order value.

• Runtime & Storage Complexity: O(n) time complexity, O(1) space complexity.

Code

    def findUnsortedSubarray(nums: list[int]) -> int:
    """
    Finds the length of the shortest unsorted continuous subarray that,
    if sorted, would make the entire array sorted.
    """

    n = len(nums)
    if n <= 1:
        return 0

    # Find the end of the unsorted subarray
    end = -1
    for i in range(n - 1):
        if nums[i] > nums[i + 1]:
            end = i + 1

    # If the array is already sorted
    if end == -1:
        return 0

    # Find the start of the unsorted subarray
    start = 0
    for i in range(n - 1, 0, -1):
        if nums[i] < nums[i - 1]:
            start = i - 1
            break

    # Find the minimum and maximum values within the unsorted subarray
    min_val = min(nums[start : end+1])
    max_val = max(nums[start : end+1])

    # Extend the start index to the left if necessary
    while start > 0 and nums[start - 1] > min_val:
        start -= 1

    # Extend the end index to the right if necessary
    while end < n - 1 and nums[end + 1] < max_val:
        end += 1

    return end - start + 1