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Beautiful Arrangement II

Updated: Apr 14, 2021

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.

Solution:

class Solution {
    public int[] constructArray(int n, int k) {
        int left=1,right=n,index=0;
        int[] res = new int[n];
        while(left<=right)
        {
            if (k>1)
            {
                res[index++]=k--%2!=0?left++:right--;
            }
            else
            {
                res[index++] = left++;
            }
        }
        return res;
    }
}

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