667

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, ... , a_n], then the list [|a₁ - a₂|, |a₂ - a₃|, |a₃ - a₄|, ... , |a_n-1 - a_n|] 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:

• Beautiful Arrangement (Medium)

Solution 1.

// OJ: https://leetcode.com/problems/beautiful-arrangement-ii/
// Author: github.com/lzl124631x
// 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/
// Author: github.com/lzl124631x
// 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;
    }
};