Introduction

In this blog post, we will explore how to solve the LeetCode problem "969" 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 of integers arr, sort the array by performing a series of pancake flips. In one pancake flip we do the following steps: Choose an integer k where 1 <= k <= arr.length. Reverse the sub-array arr[0...k-1] (0-indexed). For example, if arr = [3,2,1,4] and we performed a pancake flip choosing k = 3, we reverse the sub-array [3,2,1], so arr = [1,2,3,4] after the pancake flip at k = 3. Return an array of the k-values corresponding to a sequence of pancake flips that sort arr. Any valid answer that sorts the array within 10 * arr.length flips will be judged as correct. Example 1: Input: arr = [3,2,4,1] Output: [4,2,4,3] Explanation: We perform 4 pancake flips, with k values 4, 2, 4, and 3. Starting state: arr = [3, 2, 4, 1] After 1st flip (k = 4): arr = [1, 4, 2, 3] After 2nd flip (k = 2): arr = [4, 1, 2, 3] After 3rd flip (k = 4): arr = [3, 2, 1, 4] After 4th flip (k = 3): arr = [1, 2, 3, 4], which is sorted. Example 2: Input: arr = [1,2,3] Output: [] Explanation: The input is already sorted, so there is no need to flip anything. Note that other answers, such as [3, 3], would also be accepted. Constraints: 1 <= arr.length <= 100 1 <= arr[i] <= arr.length All integers in arr are unique (i.e. arr is a permutation of the integers from 1 to arr.length).

Explanation

Here's the solution to the pancake sorting problem:

• Iterative Placement: Iteratively place the largest unsorted element at its correct position (the end of the unsorted portion of the array).
• Two Flips: For each largest element, first flip it to the beginning of the array, and then flip the array up to its correct sorted position.

• Termination: The process continues until the entire array is sorted.

• Runtime Complexity: O(n^2), Storage Complexity: O(n), where n is the length of the input array.

Code

    def pancakeSort(arr):
    flips = []
    n = len(arr)

    for i in range(n, 0, -1):
        # Find the index of the maximum element in the unsorted portion
        max_index = arr.index(i)

        # If the maximum element is not already in its correct position
        if max_index != i - 1:
            # Flip to bring the maximum element to the front
            if max_index != 0:
                flips.append(max_index + 1)
                arr[:max_index + 1] = arr[:max_index + 1][::-1]

            # Flip to put the maximum element in its correct sorted position
            flips.append(i)
            arr[:i] = arr[:i][::-1]

    return flips