How do you solve Pancake Sorting on LeetCode?

Pancake Sorting (LeetCode #969) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Pancake sorting is a greedy algorithm that focuses on placing the largest unsorted element in its correct position.

What is the brute force solution for Pancake Sorting?

The brute force approach for Pancake Sorting is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute-force approach involves repeatedly finding the largest unsorted element and flipping it to the front, then flipping it to its correct position. This method is straightforward but inefficient. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Pancake Sorting?

Pancake Sorting uses the following concepts: Array, Two Pointers, Greedy, Sorting. The recommended patterns to study are: Greedy, Two Pointers.

What are the interview tips for Pancake Sorting?

Always think about edge cases, such as an already sorted array or an array with only one element. Explain your thought process clearly while coding, as communication is key in interviews. Practice explaining the time and space complexity of your solution to demonstrate your understanding.

What are common mistakes when solving Pancake Sorting?

Not considering the case when the array is already sorted, leading to unnecessary flips. Failing to correctly implement the flip operation, which can lead to incorrect results.

#969

Pancake Sorting

Medium

ArrayTwo PointersGreedySortingGreedyTwo Pointers

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

💡

Intuition

Time O(n)Space O(n)

The optimal solution involves iteratively placing the largest unsorted element in its correct position using a two-step flip process, minimizing the number of flips required.

⚙️

Algorithm

3 steps

1Step 1: Iterate through the array from the last element to the first.
2Step 2: For each element, find the index of the maximum element in the unsorted portion.
3Step 3: If the maximum element is not in its correct position, perform a flip to bring it to the front, then flip it to its correct position.

solution.py15 lines

1def pancakeSort(arr):
2    def flip(k):
3        arr[:k] = arr[:k][::-1]
4
5    res = []
6    n = len(arr)
7    for i in range(n, 1, -1):
8        max_index = arr.index(max(arr[:i]))
9        if max_index != i - 1:
10            if max_index != 0:
11                flip(max_index + 1)
12                res.append(max_index + 1)
13            flip(i)
14            res.append(i)
15    return res

ℹ

Complexity note: The optimal solution runs in O(n) time because we only need to find the maximum element and flip it to its correct position in a single pass, and we use additional space for the result.

1Pancake sorting is a greedy algorithm that focuses on placing the largest unsorted element in its correct position.
2The two-step flip process minimizes the number of flips needed to sort the array.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.