题解 | #牛群排队#
牛群排队
https://www.nowcoder.com/practice/8d8ae3937cd5466eb330ca484ca5ed80
import java.util.*; public class Solution { /** * 代码中的类名、方法名、参数名已经指定,请勿修改,直接返回方法规定的值即可 * * * @param nums int整型一维数组 * @return int整型二维数组 */ public int[][] cow_permute (int[] nums) { // write code here Arrays.sort(nums); reverseArray(nums); List<int[]> result = new ArrayList<>(); do { result.add(nums.clone()); } while (prevPermutation(nums)); int[][] resArray = new int[result.size()][]; for (int i = 0; i < result.size(); i++) { resArray[i] = result.get(i); } return resArray; } private boolean prevPermutation(int[] nums) { int n = nums.length; int i = n - 2; while (i >= 0 && nums[i] <= nums[i + 1]) { i--; } if (i < 0) { return false; } int j = n - 1; while (j >= 0 && nums[i] <= nums[j]) { j--; } swap(nums, i, j); reverseArray(nums, i + 1, n - 1); return true; } private void swap(int[] nums, int i, int j) { int temp = nums[i]; nums[i] = nums[j]; nums[j] = temp; } private void reverseArray(int[] nums, int start, int end) { while (start < end) { swap(nums, start, end); start++; end--; } } private void reverseArray(int[] nums) { int start = 0; int end = nums.length - 1; while (start < end) { swap(nums, start, end); start++; end--; } } }
知识点
回溯
解题分析
考查的是全排列问题,题目中已说明无重复元素,故我们在遍历时就可以对已经遍历过的元素进行判断,若已存在则跳过,直至整个数组的元素存入列表中。
编程语言:
java