LeetCode 667 - Beautiful Arrangement II

https://leetcode.com/problems/beautiful-arrangement-ii

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:

1. The n and k are in the range 1 <= k < n <= 104.

https://discuss.leetcode.com/topic/101113/c-java-clean-code-4-liner

if you have n number, the maximum k can be n - 1;
if n is 9, max k is 8.
This can be done by picking numbers interleavingly from head and tail,

// start from i = 1, j = n;
// i++, j--, i++, j--, i++, j--

1   2   3   4   5
  9   8   7   6
out: 1 9 2 8 3 7 6 4 5
dif:  8 7 6 5 4 3 2 1

This is a case where k is exactly n - 1
When k is less than that, simply lay out the rest (i, j) in incremental
order(all diff is 1). Say if k is 5:

i++, j--, i++, j--, i++, i++, i++ ...
1   9   2   8    3 4 5 6 7
  8   7   6   5    1 1 1 1 

    public int[] constructArray(int n, int k) {
        int[] res = new int[n];
        for (int i = 0, l = 1, r = n; l <= r; i++)
            res[i] = k > 1 ? (k-- % 2 != 0 ? l++ : r--) : (k % 2 != 0? l++ : r--);
        return res;
    }