# 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();
}
}```