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:
\n\nk where 1 <= k <= arr.length.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.
\n
Example 1:
\n\n\nInput: arr = [3,2,4,1]\nOutput: [4,2,4,3]\nExplanation: \nWe perform 4 pancake flips, with k values 4, 2, 4, and 3.\nStarting state: arr = [3, 2, 4, 1]\nAfter 1st flip (k = 4): arr = [1, 4, 2, 3]\nAfter 2nd flip (k = 2): arr = [4, 1, 2, 3]\nAfter 3rd flip (k = 4): arr = [3, 2, 1, 4]\nAfter 4th flip (k = 3): arr = [1, 2, 3, 4], which is sorted.\n\n\n
Example 2:
\n\n\nInput: arr = [1,2,3]\nOutput: []\nExplanation: The input is already sorted, so there is no need to flip anything.\nNote that other answers, such as [3, 3], would also be accepted.\n\n\n
\n
Constraints:
\n\n1 <= arr.length <= 1001 <= arr[i] <= arr.lengtharr are unique (i.e. arr is a permutation of the integers from 1 to arr.length).Compiled with clang 11 using the latest C++ 20 standard.
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