public class Solution
extends Object
405 - Convert a Number to Hexadecimal\.
Easy
Given an integer `num`, return _a string representing its hexadecimal representation_. For negative integers, [two’s complement](https://en.wikipedia.org/wiki/Two%27s_complement) method is used.
All the letters in the answer string should be lowercase characters, and there should not be any leading zeros in the answer except for the zero itself.
**Note:** You are not allowed to use any built-in library method to directly solve this problem.
**Example 1:**
**Input:** num = 26
**Output:** "1a"
**Example 2:**
**Input:** num = -1
**Output:** "ffffffff"
**Constraints:**
* -231 <= num <= 231 - 1