667. 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.

 

使 | a1 - a2 | | a2 - a3 | | a3 - a4 |…an-1正好有k个不同的整数

a1，a2，a3....为1-n不同的整数

 

C++（30ms）：

class Solution {
public:
    vector<int> constructArray(int n, int k) {
        vector<int> res ;
        int j = n ;
        for(int i = 1 ; i <= j ;){
            if (k > 1){
                res.push_back(k-- % 2 ? i++ : j--) ;
            }else{
                res.push_back(i++) ;
            }
        }
        return res ;
    }
};