# 667. Beautiful Arrangement II 优美的排列 II

@TOC

## # 题目描述

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.

## # 解题方法

``````class Solution(object):
def constructArray(self, n, k):
"""
:type n: int
:type k: int
:rtype: List[int]
"""
a = list(range(1, n + 1))
for i in range(1, k):
a[i:] = a[:i-1:-1]
return a
``````

``````class Solution(object):
def constructArray(self, n, k):
"""
:type n: int
:type k: int
:rtype: List[int]
"""
res = []
l, r = 1, n
while l <= r:
if k > 1:
if k % 2 == 1:
res.append(l)
l += 1
else:
res.append(r)
r -= 1
k -= 1
else:
res.append(l)
l += 1
return res
``````

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

## # 日期

2018 年 3 月 4 日 2018 年 12 月 15 日 —— 今天四六级