Given an integer, write an algorithm to convert it to hexadecimal. For negative integer, two’s complement method is used.
a-f) must be in lowercase.
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.
Input: 26 Output: "1a"
Input: -1 Output: "ffffffff"