405. Convert a Number to Hexadecimal (Easy)

Given an integer, write an algorithm to convert it to hexadecimal. For negative integer,[two’s complement]([[https://en.wikipedia.org/wiki/Two's_complement)method](https://en.wikipedia.org/wiki/Two's_complement)method](https://en.wikipedia.org/wiki/Two's_complement)method](https://en.wikipedia.org/wiki/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

Example1:
Input:
26

Output:
"1a"


Example2:
Input:
-1

Output:
"ffffffff"

/*
Basic idea: each time we take a look at the last four digits of
            binary verion of the input, and maps that to a hex char
            shift the input to the right by 4 bits, do it again
            until input becomes 0.

*/

public class Solution {
    char[] map = {'0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f'};

    public String toHex(int num) {
        if(num == 0) 
           return "0";

        String result = "";
        while(num != 0){
            result = map[(num & 15)] + result; 
            num = (num >>> 4);
        }
        return result;
    }

}