g0601_0700.s0667_beautiful_arrangement_ii.Solution Maven / Gradle / Ivy

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package g0601_0700.s0667_beautiful_arrangement_ii;

// #Medium #Array #Math #2022_03_22_Time_1_ms_(84.62%)_Space_42.4_MB_(81.82%)

/**
 * 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, ... , a_n], then the list [|a₁ - a₂|, |a₂ - a₃|, |a₃ - a₄|, ... , |a_n-1 - a_n|] 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
**/
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;
    }
}