405. Convert a Number to Hexadecimal #

Problem #

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"

Problem Summary #

Given an integer, write an algorithm to convert this number to hexadecimal. For negative integers, we usually use the two’s complement method.

Note:

1. All letters in hexadecimal (a-f) must be lowercase.
2. The hexadecimal string must not contain extra leading zeros. If the number to be converted is 0, it is represented by a single character ‘0’; otherwise, the first character in the hexadecimal string will not be the 0 character. 
3. The given number is guaranteed to be within the range of a 32-bit signed integer.
4. You must not use any library-provided method that directly converts or formats the number to hexadecimal.

Solution Ideas #

• This problem is easy: convert a decimal number into a hexadecimal number. Extra attention is needed for the cases of 0 and negative numbers.

Code #

package leetcode

func toHex(num int) string {
	if num == 0 {
		return "0"
	}
	if num < 0 {
		num += 1 << 32
	}
	mp := map[int]string{
		0: "0", 1: "1", 2: "2", 3: "3", 4: "4", 5: "5", 6: "6", 7: "7", 8: "8", 9: "9",
		10: "a", 11: "b", 12: "c", 13: "d", 14: "e", 15: "f",
	}
	var bitArr []string
	for num > 0 {
		bitArr = append(bitArr, mp[num%16])
		num /= 16
	}
	str := ""
	for i := len(bitArr) - 1; i >= 0; i-- {
		str += bitArr[i]
	}
	return str
}