667. Beautiful Arrangement II

问题：

给定一个n，有数组1～n，

排列该数组，使得数组两两元素之间的差值有k种。

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:
The n and k are in the range 1 <= k < n <= 104.

　　

解法：

如有以下数组

[1,2,3,4,5,6,7,8,9,10]

　　

n=10, 

k=9的情况，则有

 i, j,  i++,  j--,   i++,  j--,  i++,  j--,   i++, j--,
[1, 10, 2,      9,    3,    8,    4,    7,     5,    6]
k= 9， 8，  7，     6，   5，    4，   3，    2，   1

　　

k=6的情况，则有

 j,  i, j--,   i++,  j--,  i++,  i++,   i++, i++,  i++
[10, 1, 9,      2,    8,    3,    4,    5,    6,    7]
k= 9， 8，  7，     6，   5，    1，   1，    1，   1

　　

代码参考：

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