Package 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 Details

    • Solution

      public Solution()

  • Method Details

    • pancakeSort

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