# Leetcode: 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"
```

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

```## Blog link: https://code.dennyzhang.com/convert-a-number-to-hexadecimal
## Basic Ideas: For negative numbers, two's complement
##        https://en.wikipedia.org/wiki/Two%27s_complement
##        -1 ---> pow(2, 32) + 1
## Complexity: Time O(k), Space O(1). k = len(result)
class Solution:
def toHex(self, num):
"""
:type num: int
:rtype: str
"""
if num == 0: return '0'
if num < 0: return self.toHex(pow(2, 32)+num)
res = ''
while num != 0:
mod_val = num%16
num = int(num/16)
if mod_val < 10:
mod_str = str(mod_val)
else:
mod_str = chr(ord('a') + mod_val-10)
# print(mod_val, mod_str)
res = '%s%s' % (mod_str, res)
return res

# s = Solution()
# print(s.toHex(-1)) # ffffffff
# print(s.toHex(26)) # 1a
```

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