667. Beautiful Arrangement II

Posted 2021-01-21 ordili

1. Question:

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.

2. Solution

class Solution:
    def constructArray(self, n, k):
        """
        :type n: int
        :type k: int
        :rtype: List[int]
        """
        re = list(range(1, n + 1))

        j = k
        right_value = k + 1
        left_value = 1
        while j > 0:
            re[j] = right_value
            re[j - 1] = left_value
            right_value -= 1
            left_value += 1
            j -= 2

        if j == 0:
            re[0] = left_value
        return re