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

解题思路：

可以想到如果排列是1-n的话差列只有1，如果将2-n旋转，则变为2，继续旋转则为3，最后排序结果为1，n,2,n-1......

class Solution {
public:
vector<int> constructArray(int n, int k) {
vector<int> ret;
int start=1;
int end = n;

for(int i=0;i<k;i++){
if(i%2==0)
ret.push_back(start++);
else ret.push_back(end--);
}
int temp = ret[k-1];
if(k%2!=0){//递增
for(int j=1;j<=n-k;j++)
ret.push_back(++temp);

}
else{
for(int j=1;j<=n-k;j++)
ret.push_back(--temp);
}
return ret;

}
};