405. Convert a Number to Hexadecimal

Given an integer, write an algorithm to convert it to hexadecimal. For negative integer, two’s complement method 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"

十进制转十六进制

C++(6ms):

 1 class Solution {
 2 public:
 3     const string HEX = "0123456789abcdef" ;
 4     string toHex(int num) {
 5         if (num == 0)
 6             return "0" ;
 7         string res = "" ;
 8         int count = 0 ;
 9         while(num && count++ < 8){
10             res = HEX[num & 0xf] + res ;
11             num >>= 4 ;
12         }
13         return res ;
14     }
15 };