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Formatted question description: https://leetcode.ca/all/667.html

# 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, ... , 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.

Related Topics:
Array

Similar Questions:

## Solution 1.

• class Solution {
public int[] constructArray(int n, int k) {
int[] sorted = new int[n];
for (int i = 0; i < n; i++)
sorted[i] = i + 1;
int[] arrangement = new int[n];
int low = 0, high = k;
for (int i = 0; i <= k; i++) {
if (i % 2 == 0)
arrangement[i] = sorted[low++];
else
arrangement[i] = sorted[high--];
}
for (int i = k + 1; i < n; i++)
arrangement[i] = sorted[i];
return arrangement;
}
}

############

class Solution {
public int[] constructArray(int n, int k) {
int l = 1, r = n;
int[] ans = new int[n];
for (int i = 0; i < k; ++i) {
ans[i] = i % 2 == 0 ? l++ : r--;
}
for (int i = k; i < n; ++i) {
ans[i] = k % 2 == 0 ? r-- : l++;
}
return ans;
}
}

• // OJ: https://leetcode.com/problems/beautiful-arrangement-ii/
// 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;
}
};

• class Solution:
def constructArray(self, n: int, k: int) -> List[int]:
l, r = 1, n
ans = []
for i in range(k):
if i % 2 == 0:
ans.append(l)
l += 1
else:
ans.append(r)
r -= 1
for i in range(k, n):
if k % 2 == 0:
ans.append(r)
r -= 1
else:
ans.append(l)
l += 1
return ans

############

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

• func constructArray(n int, k int) []int {
l, r := 1, n
ans := make([]int, n)
for i := 0; i < k; i++ {
if i%2 == 0 {
ans[i] = l
l++
} else {
ans[i] = r
r--
}
}
for i := k; i < n; i++ {
if k%2 == 0 {
ans[i] = r
r--
} else {
ans[i] = l
l++
}
}
return ans
}

• function constructArray(n: number, k: number): number[] {
let l = 1;
let r = n;
const ans = new Array(n);
for (let i = 0; i < k; ++i) {
ans[i] = i % 2 == 0 ? l++ : r--;
}
for (let i = k; i < n; ++i) {
ans[i] = k % 2 == 0 ? r-- : l++;
}
return ans;
}