[Swift]LeetCode405. 數字轉換爲十六進制數 | Convert a Number to Hexadecimal

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Given an integer, write an algorithm to convert it to hexadecimal. For negative integer, two’s complementmethod is used.

Note:

1. All letters in hexadecimal (a-f) must be in lowercase.
2. The hexadecimal string must not contain extra leading 0s. If the number is zero, it is represented by a single zero character '0'; otherwise, the first character in the hexadecimal string will not be the zero character.
3. The given number is guaranteed to fit within the range of a 32-bit signed integer.
4. You must not use any method provided by the library which converts/formats the number to hex directly. 

Example 1:

Input:
26

Output:
"1a"

Example 2:

Input:
-1

Output:
"ffffffff"

---

給定一個整數，編寫一個算法將這個數轉換爲十六進制數。對於負整數，咱們一般使用 補碼運算 方法。

注意:

1. 十六進制中全部字母(a-f)都必須是小寫。
2. 十六進制字符串中不能包含多餘的前導零。若是要轉化的數爲0，那麼以單個字符'0'來表示；對於其餘狀況，十六進制字符串中的第一個字符將不會是0字符。 
3. 給定的數確保在32位有符號整數範圍內。
4. 不能使用任何由庫提供的將數字直接轉換或格式化爲十六進制的方法。

示例 1：

輸入:
26

輸出:
"1a"

示例 2：

輸入:
-1

輸出:
"ffffffff"

---

8ms

 1 class Solution {
 2     var hex:String = "0123456789abcdef"
 3     func toHex(_ num: Int) -> String {
 4         if num == 0 {return "0"}
 5         var number:Int = num
 6         var result:String = ""
 7         var count:Int = 0
 8         while(number != 0 && count < 8)
 9         {
10             var index = hex.index(hex.startIndex,offsetBy: (number & 0xf))
11             result.insert(hex[index],at: result.startIndex)
12             //注意符號：>>=
13             number >>= 4
14             count += 1
15         }
16         return result
17     }
18 }

---

8ms

 1 class Solution {
 2     func toHex(_ num: Int) -> String {
 3     var result = ""
 4     var map = [10:"a", 11:"b", 12:"c", 13:"d", 14:"e", 15:"f"]
 5     
 6     let base = 16
 7     var tmp = num
 8     
 9     if tmp < 0 {
10         tmp += 2 << 31
11     } else if tmp == 0 {
12         return "0"
13     }
14     
15     while tmp != 0 {
16         let mod = tmp % base
17         tmp = tmp / base
18         
19         if mod < 10 {
20             result = String(mod) + result
21         } else {
22             if let value = map[mod] {
23                 result = value + result
24             }
25         }
26     }
27     
28     return result
29     }
30 }

---

12ms

 1 class Solution {
 2     func toHex(_ num: Int) -> String {
 3         guard num != 0 else {
 4             return "0"
 5         }
 6 
 7         let map = ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f"]
 8         var result = ""
 9         var num = num < 0 ? Int(UInt32.max) + num + 1 : num
10         while num > 0 {
11             result = map[num % 16] + result
12             num /= 16
13         }
14 
15         return result
16     }
17 }

---

12ms

 1 class Solution {
 2     func toHex(_ num: Int) -> String {
 3         let map = ["0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f"]
 4         if num > 0 {
 5             var temp = num
 6             var res = ""
 7             while temp != 0 {
 8                 let v = temp & 15 
 9                 res = map[v] + res
10                 temp >>= 4
11             }
12             return res
13         } else if num == 0 {
14             return "0"
15         } else {
16             var res = ""
17             for i in 0..<8 {
18                 let v = num & (15 << (i*4))
19                 res = map[v>>(i*4)] + res
20             }
21             return res
22         }
23     }
24 }

---

16ms

 1 class Solution {
 2     func toHex(_ num: Int) -> String {
 3         if num == 0 {
 4             return "0"
 5         }
 6 
 7         let map = ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f"]
 8         var num = num
 9         var res = ""
10         var i = 0
11 
12         while num != 0 && i < 8 {
13             res = map[num & 0b1111] + res
14             num >>= 4
15             i += 1
16         }
17 
18         return res
19     }
20 }