Suppose you have N integers from 1 to N. We define a beautiful arrangement as an array that is constructed by these N numbers successfully if one of the following is true for the ith position (1 <= i <= N) in this array: The number at the ith positi…

public class Solution { //回溯法 //根据回溯的思路,同样,可以对本题的Beautiful排列实现. //比如,当N为5时,使用回溯算法先是得到(1,2,3,4,5)排列,符合要求,符合要求的排列数count+1, //接着回溯到第四个位置,在剩下的选择中选5,但发现5不符合要求,然后跳过,不再往后判断. //同样当得到(1,2,5)这前三个排列时,5已经不符合要求,也不会再往后判断(1,2,5,x,x). //这样减少了直接穷举递归方法中很多不需要判断操作,提高了效率…