405. 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 `0`s. 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"
```

405. Convert a Number to Hexadecimal
``````struct Solution;

#[allow(clippy::wrong_self_convention)]
impl Solution {
fn to_hex(num: i32) -> String {
format!("{:x}", num)
}
}

#[test]
fn test() {
let num = -1;
let res = "ffffffff";
assert_eq!(Solution::to_hex(num), res);
}
``````