667. Beautiful Arrangement II

Posted 2021-02-14 ruruozhenhao

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.

 

Approach #1: Math. [Java]

class Solution {
    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--) : l++;
        }
        
        return res;
    }
}

　　

Analysis:

https://leetcode.com/problems/beautiful-arrangement-ii/discuss/106948/C%2B%2B-Java-Clean-Code-4-liner