667. 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.
class Solution(object):
    def constructArray(self, n, k):
        """
        :type n: int
        :type k: int
        :rtype: List[int]
        """
        def construct(k):
            
            nums = set(range(2,k+2))
            ans = [1]
            
            for d in range(k,0,-1):
                if ans[-1] + d in nums:
                    nums.remove(ans[-1] + d)
                    ans.append(ans[-1] + d)
                else:
                    nums.remove(ans[-1] - d)
                    ans.append(ans[-1] - d)
                    
                    
            return ans
        
        return construct(k) + range(k+2,n+1)

 

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