[Swift]LeetCode667. 优美的排列 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.

---

给定两个整数 n 和 k，你需要实现一个数组，这个数组包含从 1 到 n 的 n 个不同整数，同时满足以下条件：

① 如果这个数组是 [a1, a2, a3, ... , an] ，那么数组 [|a1 - a2|, |a2- a3|, |a3 - a4|, ... , |an-1 - an|] 中应该有且仅有 k 个不同整数；.

② 如果存在多种答案，你只需实现并返回其中任意一种.

示例 1:

输入: n = 3, k = 1
输出: [1, 2, 3]
解释: [1, 2, 3] 包含 3 个范围在 1-3 的不同整数， 并且 [1, 1] 中有且仅有 1 个不同整数 : 1 

示例 2:

输入: n = 3, k = 2
输出: [1, 3, 2]
解释: [1, 3, 2] 包含 3 个范围在 1-3 的不同整数， 并且 [2, 1] 中有且仅有 2 个不同整数: 1 和 2 

提示:

1.  n 和 k 满足条件 1 <= k < n <= 10^4.

---

Runtime: 28 ms

Memory Usage: 19 MB

class Solution {
    func constructArray(_ n: Int, _ k: Int) -> [Int] {
        var k = k
        var res:[Int] = [Int]()
        var i:Int = 1
        var j:Int = n
        while (i <= j)
        {
            var num:Int = 0
            if k > 1
            {
                if k % 2 != 0
                {
                    num = i
                    i += 1 
                }
                else
                {
                    num = j
                    j -= 1
                }
                k -= 1                               
            }
            else
            {
                num = i
                i += 1 
            }
            res.append(num)
        }        
        return res
    }
}

---

36ms

class Solution {
    func constructArray(_ n: Int, _ k: Int) -> [Int] {
        var res = Array(repeating: 0, count: n)
        var l = 1, r = n
        for i in 0..<k {
            if i % 2 == 0 {
                res[i] = l
                l += 1
            } else {
                res[i] = r
                r -= 1
            }
        }
        if k % 2 == 1 {
            for i in k..<n {
                res[i] = l
                l += 1
            }            
        } else {
            for i in k..<n {
                res[i] = r
                r -= 1
            }              
        }

        return res
    }
}

---

44ms

class Solution {
    func constructArray(_ n: Int, _ k: Int) -> [Int] {
        if k == 1 { return Array(1 ... n) }
        
        func gen(_ k: Int) -> [Int] {
            var ret = Array(repeating: 0, count: k)
            for i in ret.indices {
                ret[i] = i % 2 == 0 ? i/2 + 1 : k - i/2
            }
            return ret
        }
        
        if k + 1 == n { return gen(n) }
        return gen(k + 1) + Array(k + 2 ... n)
    }
}

---

60ms

class Solution {
    func constructArray(_ n: Int, _ k: Int) -> [Int] {
        var result = [Int](repeating: 0, count: n)
        
        var j = 0
        for i in 0..<(n - k - 1) {
            result[i] = i + 1
            j += 1
        }
        
        for i in 0...k {
            result[j] = i % 2 == 0 
                ? n - k + i / 2
                : n - i / 2
            j += 1
        }
        
        return result
    }
}