Given an array A, we can perform a pancake flip: We choose
some positive integer k <= A.length, then reverse the
order of the first k elements of A. We want to perform
zero or more pancake flips (doing them one after another in succession) to sort the array
A.
Return the k-values corresponding to a sequence of pancake flips that sort A.
Any valid answer that sorts the array within 10 * A.length flips will be
judged as correct.
Example 1:
Input: [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: A = [3, 2, 4, 1] After 1st flip (k=4): A = [1, 4, 2, 3] After 2nd flip (k=2): A = [4, 1, 2, 3] After 3rd flip (k=4): A = [3, 2, 1, 4] After 4th flip (k=3): A = [1, 2, 3, 4], which is sorted.
Example 2:
Input: [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.