Convert a Number to Hexadecimal

update Jan 13,2018 20:17

LeetCode

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"

Basic Idea

基本思路就是用一个长度为 16 的 string 数组来map每一对 <number, char>，然后四位四位读 input integer，按顺序append到stringbuilder中。

Java Code:

    class Solution {
        public String toHex(int num) {
            if (num == 0) return "0";
            char[] hex = "0123456789abcdef".toCharArray();
            int mask = 0b1111;
            StringBuilder sb = new StringBuilder();
            while (num != 0) {
                int digit = num & mask;
                num >>>= 4;
                sb.append(hex[digit]);
            }
            return sb.reverse().toString();
        }
    }