405. Convert a Number to Hexadecimal （将一个数转换为16进制表示）

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"

public class Solution {
    public String toHex(int num) {
        StringBuilder sb = new StringBuilder();
		int hex;
		do {
			hex = num & 0x0000000f;
			if (hex < 10)
				sb.insert(0, (char) (hex + '0'));
			else
				sb.insert(0, (char) (hex - 10 + 'a'));
			num >>>= 4;
		} while (num != 0);
		return sb.toString();
    }
}