leetcode 405. Convert a Number to Hexadecimal(十进制转十六进制>>>)

问题描述：

  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.

思路：

  可以每4位进行按位与，得到的数字对应十六进制的对应表示，然后将num无符号右移>>>4位，继续进行按位与操作。

代码：

class Solution {    public String toHex(int num) {        if (num == 0) return "0";        char[] refer = {'0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f'};        String result = "";        while(num != 0){            result = refer[(num & 15)] + result;            num >>>= 4;        }        return result;    }}