Beautiful Arrangement II Python Solution

lcpy gen -n 667   # by problem number
lcpy gen -s beautiful_arrangement_ii   # by problem name

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.

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.

class Solution:
    # Zig-zag the first k+1 values between the low and high ends: the k gaps of that
    # prefix are exactly k, k-1, ..., 1, then a plain ascending run keeps only 1.
    # Time: O(n)
    # Space: O(1) extra besides the output list
    def construct_array(self, n: int, k: int) -> list[int]:
        result: list[int] = []
        low, high = 1, k + 1
        while low < high:
            result.extend([low, high])
            low += 1
            high -= 1
        if low == high:
            result.append(low)
        result.extend(range(k + 2, n + 1))
        return result