[Swift]LeetCode1017. 负二进制转换 | Convert to Base -2

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Given a number N, return a string consisting of "0"s and "1"s that represents its value in base -2 (negative two).

The returned string must have no leading zeroes, unless the string is "0". 

Example 1:

Input: 2
Output: "110" Explantion: (-2) ^ 2 + (-2) ^ 1 = 2 

Example 2:

Input: 3
Output: "111" Explantion: (-2) ^ 2 + (-2) ^ 1 + (-2) ^ 0 = 3 

Example 3:

Input: 4
Output: "100" Explantion: (-2) ^ 2 = 4 

Note:

1. 0 <= N <= 10^9

---

给出数字 N，返回由若干 "0" 和 "1"组成的字符串，该字符串为 N 的负二进制（base -2）表示。

除非字符串就是 "0"，不然返回的字符串中不能含有前导零。 

示例 1：

输入：2
输出："110"
解释：(-2) ^ 2 + (-2) ^ 1 = 2

示例 2：

输入：3
输出："111"
解释：(-2) ^ 2 + (-2) ^ 1 + (-2) ^ 0 = 3

示例 3：

输入：4
输出："100"
解释：(-2) ^ 2 = 4 

提示：

1. 0 <= N <= 10^9

---

8ms

 1 class Solution {
 2     func baseNeg2(_ N: Int) -> String {
 3         var num = N
 4         var str = ""
 5         var base = -2
 6         while num < 0 || num >= 2 {
 7             var q = Int(num / base)
 8             if num < 0, num % base != 0 { q += 1 }
 9             str = "\((num - q * base))\(str)"
10             num = q
11         }
12         if num != 0 {
13             str = "\(num)\(str)"
14         }
15         if str.isEmpty {
16             str = "0"
17         }
18         return str
19     }
20 }

---

Runtime: 16 ms

Memory Usage: 18.9 MB

 1 class Solution {
 2     func baseNeg2(_ N: Int) -> String {
 3         var N = N
 4         var ans:String = String()
 5         while(N != 0)
 6         {
 7             var r:Int = abs(N % 2)
 8             if r != 0 { N -= 1}
 9             var q:Int = N / -2
10             ans.append((r + 48).ASCII)
11             N = q            
12         }
13         ans = String(ans.reversed())
14         if ans.isEmpty
15         {
16             ans.append("0")
17         }
18         return ans        
19     }
20 }
21 
22 //Int扩展
23 extension Int
24 {
25     //Int转Character,ASCII值(定义大写为字符值)
26     var ASCII:Character 
27     {
28         get {return Character(UnicodeScalar(self)!)}
29     }
30 }