README.md

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 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"

Solutions (Python)

1. Two's Complement

class Solution:
    def toHex(self, num: int) -> str:
        hex_ch = "0123456789abcdef"
        hex_n = ""

        if num == 0:
            return "0"
        elif num > 0:
            while num > 0:
                hex_n += hex_ch[num % 16]
                num //= 16
        elif num < 0:
            num = -num
            plus_one = True

            while num > 0:
                if plus_one and num % 16 != 0:
                    hex_n += hex_ch[15 - num % 16 + 1]
                    plus_one = False
                elif plus_one:
                    hex_n += '0'
                else:
                    hex_n += hex_ch[15 - num % 16]
                num //= 16

            hex_n += 'f' * (8 - len(hex_n))

        return hex_n[::-1]

2. Convert to Unsigned Integer

class Solution:
    def toHex(self, num: int) -> str:
        hex_ch = "0123456789abcdef"
        hex_n = ""

        if num == 0:
            return "0"
        elif num < 0:
            num = 4294967296 + num

        while num > 0:
            hex_n += hex_ch[num % 16]
            num //= 16

        return hex_n[::-1]

3. Bitwise Operator

class Solution:
    def toHex(self, num: int) -> str:
        hex_ch = "0123456789abcdef"
        hex_n = ""

        if num == 0:
            return "0"

        if num < 0:
            num &= 0x7fffffff
            hex_n += hex_ch[num & 0xf]
            num >>= 4
            num |= 0x08000000

        while num != 0:
            hex_n += hex_ch[num & 0xf]
            num >>= 4

        return hex_n[::-1]