[LeetCode] 405. Convert a Number to Hexadecimal

题：https://leetcode.com/problems/convert-a-number-to-hexadecimal/description/

题目

Given an integer, write an algorithm to convert it to hexadecimal. For negative integer, two’s complement method is used.

Note:

All letters in hexadecimal (a-f) must be in lowercase.
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.
The given number is guaranteed to fit within the range of a 32-bit signed integer.
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"

题目大意

将 num 变为 补码形式，然后求其 十六进制的格式。

思路

由于 是 十六进制的，所以可以 直接用 位运算。

同时 是 补发，所以 使用 非符号右移。

class Solution {
    static char[] map  = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
    
    public String toHex(int num) {
        StringBuilder strBuilder = new StringBuilder();
        do{
            strBuilder.append(map[num & 0b1111]);
            num = num>>>4;            
        }while(num>0);
        return strBuilder.reverse().toString()   
    }
}