Formatted question description: https://leetcode.ca/all/667.html

667. Beautiful Arrangement II (Medium)

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.

Related Topics:
Array

Similar Questions:

Solution 1.

// OJ: https://leetcode.com/problems/beautiful-arrangement-ii/

// Time: O(N)
// Space: O(1)
class Solution {
public:
    vector<int> constructArray(int n, int k) {
        vector<int> ans(n);
        for (int i = 0, val = 1, diff = k, dir = 1; i < n; ++i) {
            ans[i] = val;
            if (diff == 0) {
                dir = 0;
                val = 2 + k;
                diff = 1; // any non-zero value
            } else if (dir) {
                val += diff * dir;
                --diff;
                dir = -dir;
            } else ++val;
        }
        return ans;
    }
};

Or

// OJ: https://leetcode.com/problems/beautiful-arrangement-ii/

// Time: O(N)
// Space: O(1)
class Solution {
public:
    vector<int> constructArray(int n, int k) {
        vector<int> ans(n, 1);
        int i = 1;
        for (int val = 1, diff = k, dir = 1; diff; ++i) {
            val += diff * dir;
            --diff;
            dir = -dir;
            ans[i] = val;
        }
        for (int val = 2 + k; i < n; ++i, ++val) ans[i] = val;
        return ans;
    }
};

Java

class Solution {
    public int[] constructArray(int n, int k) {
        int[] sorted = new int[n];
        for (int i = 0; i < n; i++)
            sorted[i] = i + 1;
        int[] arrangement = new int[n];
        int low = 0, high = k;
        for (int i = 0; i <= k; i++) {
            if (i % 2 == 0)
                arrangement[i] = sorted[low++];
            else
                arrangement[i] = sorted[high--];
        }
        for (int i = k + 1; i < n; i++)
            arrangement[i] = sorted[i];
        return arrangement;
    }
}

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