405. Convert a Number to Hexadecimal

Given an integer, write an algorithm to convert it to hexadecimal. For negative integer, two’s complementmethod 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"

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 res = "";
        while(num != 0){
            res = map[num & 16] + res ; // num %16 == num & 15 考虑符号
            num = num >>> 4;  //类似 num ／ 16 num>>> 4 考虑符号位
        }
        return res;
    }
}