LeetCode 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:
All letters in hexadecimal (

a-f

) must be in lowercase.
The hexadecimal string must not contain extra leading 

0

s. 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.
The given number is guaranteed to fit within the range of a 32-bit signed integer.
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"

Runtime: 7 ms

static char[] digits = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};

public String toHex(int num) {
return num >>> 4 == 0 ? String.valueOf(digits[num & 0xf]) : toHex(num >>> 4) + digits[num & 0xf];
}

public String toHex2(int num) {
String hexs = new String();
while (num != 0) {
hexs = digits[num & 0xf] + hexs;
num = num >>> 4;
}
return hexs.length() == 0 ? "0" : hexs;
}