原题链接在这里：https://leetcode.com/problems/beautiful-arrangement-ii/description/
题目：
Given two integers n and k, you need to construct a list which contains n different positive integers ranging from 1 to n and obeys the following requirement:
Suppose this list is [a1, a2, a3, ... , an], then the list [|a1 - a2|, |a2 - a3|, |a3 - a4|, ... , |an-1 - an|] has exactly k distinct integers.
If there are multiple answers, print any of them.
Example 1:
Input: n = 3, k = 1 Output: [1, 2, 3] Explanation: The [1, 2, 3] has three different positive integers ranging from 1 to 3, and the [1, 1] has exactly 1 distinct integer: 1.
Example 2:
Input: n = 3, k = 2 Output: [1, 3, 2] Explanation: The [1, 3, 2] has three different positive integers ranging from 1 to 3, and the [2, 1] has exactly 2 distinct integers: 1 and 2.
Note:
- The
nandkare in the range 1 <= k < n <= 104.
题解：
头k-1个数按照1, n, 2, n-1, 3, n-2...的规律, diff的绝对值是n-1, n-2, n-3减小. 剩下的部分都按照diff是1增长.
Time Complexity: O(n).
Space: O(n), res space.
AC Java:
1 class Solution { 2 public int[] constructArray(int n, int k) { 3 int [] res = new int[n]; 4 int l = 1; 5 int r = n; 6 int i = 0; 7 while(l<=r){ 8 res[i] = (k <= 1) ? l++ : (k%2 == 1 ? l++ : r--); 9 k--; 10 i++; 11 } 12 return res; 13 } 14 }