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### 题目描述

Given an array of integers A, We need to sort the array performing a series of pancake flips.

In one pancake flip we do the following steps:

• Choose an integer k where 0 <= k < A.length.
• Reverse the sub-array A[0…k].
For example, if A = [3,2,1,4] and we performed a pancake flip choosing k = 2, we reverse the sub-array [3,2,1], so A = [1,2,3,4] after the pancake flip at k = 2.

Return an array of the k-values of the pancake flips that should be performed in order to sort A. Any valid answer that sorts the array within 10 * A.length flips will be judged as correct.

### 例子

#### 例子 1

Input: A = [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.
Notice that we return an array of the chosen k values of the pancake flips.

#### 例子 2

Input: A = [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.

### Note

• `1 <= A.length <= 100`
• `1 <= A[i] <= A.length`
• All integers in `A` are unique (i.e. `A` is a permutation of the integers from `1` to `A.length`).

• 时间复杂度：O(n^2)
• 空间复杂度：O(1)