Leetcode: Convert a Number to Hexadecimal

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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