[Swift]LeetCode667. 優美的排列 II | Beautiful Arrangement II

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Given two integers n and k, you need to construct a list which contains n different positive integers ranging from 1to 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 <= 10^4.

---

給定兩個整數 n 和 k，你須要實現一個數組，這個數組包含從 1 到 n 的 n 個不一樣整數，同時知足如下條件：

① 若是這個數組是 [a1, a2, a3, ... , an] ，那麼數組 [|a1 - a2|, |a2- a3|, |a3 - a4|, ... , |an-1 - an|] 中應該有且僅有 k 個不一樣整數；.

② 若是存在多種答案，你只需實現並返回其中任意一種.

示例 1:

輸入: n = 3, k = 1
輸出: [1, 2, 3]
解釋: [1, 2, 3] 包含 3 個範圍在 1-3 的不一樣整數， 而且 [1, 1] 中有且僅有 1 個不一樣整數 : 1 

示例 2:

輸入: n = 3, k = 2
輸出: [1, 3, 2]
解釋: [1, 3, 2] 包含 3 個範圍在 1-3 的不一樣整數， 而且 [2, 1] 中有且僅有 2 個不一樣整數: 1 和 2 

提示:

1.  n 和 k 知足條件 1 <= k < n <= 10^4.

---

Runtime: 28 ms

Memory Usage: 19 MB

 1 class Solution {
 2     func constructArray(_ n: Int, _ k: Int) -> [Int] {
 3         var k = k
 4         var res:[Int] = [Int]()
 5         var i:Int = 1
 6         var j:Int = n
 7         while (i <= j)
 8         {
 9             var num:Int = 0
10             if k > 1
11             {
12                 if k % 2 != 0
13                 {
14                     num = i
15                     i += 1 
16                 }
17                 else
18                 {
19                     num = j
20                     j -= 1
21                 }
22                 k -= 1                               
23             }
24             else
25             {
26                 num = i
27                 i += 1 
28             }
29             res.append(num)
30         }        
31         return res
32     }
33 }

---

36ms

 1 class Solution {
 2     func constructArray(_ n: Int, _ k: Int) -> [Int] {
 3         var res = Array(repeating: 0, count: n)
 4         var l = 1, r = n
 5         for i in 0..<k {
 6             if i % 2 == 0 {
 7                 res[i] = l
 8                 l += 1
 9             } else {
10                 res[i] = r
11                 r -= 1
12             }
13         }
14         if k % 2 == 1 {
15             for i in k..<n {
16                 res[i] = l
17                 l += 1
18             }            
19         } else {
20             for i in k..<n {
21                 res[i] = r
22                 r -= 1
23             }              
24         }
25 
26         return res
27     }
28 }

---

44ms

 1 class Solution {
 2     func constructArray(_ n: Int, _ k: Int) -> [Int] {
 3         if k == 1 { return Array(1 ... n) }
 4         
 5         func gen(_ k: Int) -> [Int] {
 6             var ret = Array(repeating: 0, count: k)
 7             for i in ret.indices {
 8                 ret[i] = i % 2 == 0 ? i/2 + 1 : k - i/2
 9             }
10             return ret
11         }
12         
13         if k + 1 == n { return gen(n) }
14         return gen(k + 1) + Array(k + 2 ... n)
15     }
16 }

---

60ms

 1 class Solution {
 2     func constructArray(_ n: Int, _ k: Int) -> [Int] {
 3         var result = [Int](repeating: 0, count: n)
 4         
 5         var j = 0
 6         for i in 0..<(n - k - 1) {
 7             result[i] = i + 1
 8             j += 1
 9         }
10         
11         for i in 0...k {
12             result[j] = i % 2 == 0 
13                 ? n - k + i / 2
14                 : n - i / 2
15             j += 1
16         }
17         
18         return result
19     }
20 }