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"

Solution:

class Solution {
    public String toHex(int num) {
        if (num == 0) return "0";
        StringBuilder sb = new StringBuilder();
        long n = num;
        if (n < 0) n += (long) 2 << 31;
        while (n != 0) {
            long r = n % 16;
            n = n / 16;
            if (r >= 10) {
                sb.append((char) (r - 10 + 'a'));
            } else {
                sb.append((char) (r + '0'));
            }
        }
        return sb.reverse().toString();
    }
}