LeetCode-in-Java

667. Beautiful Arrangement II

Medium

Given two integers n and k, construct a list answer that contains n different positive integers ranging from 1 to n and obeys the following requirement:

• Suppose this list is answer = [a1, a2, a3, ... , an], then the list [|a1 - a2|, |a2 - a3|, |a3 - a4|, ... , |an-1 - an|] has exactly k distinct integers.

Return the list answer. If there multiple valid answers, return 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.

Constraints:

• 1 <= k < n <= 104

Solution

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

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