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Description:
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 position is divisible by i.
i is divisible by the number at the ith position.
Now given N, how many beautiful arrangements can you construct?
Example 1:
Input: 2
Output: 2
Explanation:
The first beautiful arrangement is [1, 2]:
Number at the 1st position (i=1) is 1, and 1 is divisible by i (i=1).
Number at the 2nd position (i=2) is 2, and 2 is divisible by i (i=2).
The second beautiful arrangement is [2, 1]:
Number at the 1st position (i=1) is 2, and 2 is divisible by i (i=1).
Number at the 2nd position (i=2) is 1, and i (i=2) is divisible by 1.
Note:
N is a positive integer and will not exceed 15.
解法：
思路是“从后向前”依次验证每一个数是否可以占这一位置。
int count = 0;public int countArrangement(int N) {helper(N, N, new int[N+1]);return count;}private void helper(int N, int pos, int[] visited) {if(pos < 2){count++;return;}for(int i=1; i<=N; i++) {if(visited[i] ==0 && (pos % i ==0 || i % pos == 0)) {visited[i] = 1;helper(N, pos - 1, visited);visited[i] = 0;}}}这篇关于leetcode526 Beautiful Arrangement Java的文章就介绍到这儿，希望我们推荐的文章对编程师们有所帮助！
