本文共 2275 字,大约阅读时间需要 7 分钟。
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
where1 <= 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 from1
toarr.length
).
题意:给你一个整数数组 arr
,请使用 煎饼翻转 完成对数组的排序。一次煎饼翻转的执行过程如下:
- 选择一个整数
k
,1 <= k <= arr.length
- 反转子数组
arr[0...k-1]
(下标从 0 开始)
以数组形式返回能使 arr
有序的煎饼翻转操作所对应的 k
值序列。任何将数组排序且翻转次数在 10 * arr.length
范围内的有效答案都将被判断为正确。
解法 排序
类似冒泡排序的思想,每次先找到剩余数组区间中的最大数组元素,然后通过翻转将其放置在区间末尾,直到整个数组都有序为止。这一做法的翻转次数最多为 2 * arr.length
,因为对每个最大数组元素,可能需要先翻转到数组首位,然后翻转到区间尾部。
class Solution { public: vector pancakeSort(vector & arr) { vector ans; for (int i = arr.size() - 1; i >= 0; --i) { int maxj = 0; for (int j = 1; j <= i; ++j) if (arr[j] > arr[maxj]) maxj = j; if (maxj == i) continue; //最大值在末尾 ans.push_back(maxj + 1); //翻转arr[0,maxj]这一区间,将最大值翻转到数组首位 reverse(arr.begin(), arr.begin() + maxj + 1); ans.push_back(i + 1); //翻转arr[0,i]这一区间,将最大值翻转到i位 reverse(arr.begin(), arr.begin() + i + 1); } return ans; }};
运行效率如下所示:
执行用时:4 ms, 在所有 C++ 提交中击败了78.95% 的用户内存消耗:10.8 MB, 在所有 C++ 提交中击败了76.12% 的用户
转载地址:https://memcpy0.blog.csdn.net/article/details/117639980 如侵犯您的版权,请留言回复原文章的地址,我们会给您删除此文章,给您带来不便请您谅解!