g0901_1000.s0969_pancake_sorting

Class Solution

java.lang.Object

g0901_1000.s0969_pancake_sorting.Solution

public class Solution
extends Object

969 - Pancake Sorting.

Medium

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).

Constructor Summary

Constructors

Constructor and Description
Solution()

Method Summary

Modifier and Type	Method and Description
List<Integer>	pancakeSort(int[] arr)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Solution

public Solution()

Method Detail

pancakeSort

public List<Integer> pancakeSort(int[] arr)