[LeetCode]405. Convert a Number to Hexadecimal

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

求一个数的十六进制补码表示

几个问题：1、能用位运算就用为预算，比如求16的余数，不要用区余操作，用&15；2、>>>是无符号右移操作，适用于部分负数的移位运算

public class Solution {
    public String toHex(int num) {
        char[] dict = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
        StringBuilder sb = new StringBuilder();
        do {
            sb.append(dict[num & 15]);
            num = num >>> 4;
        } while (num != 0);
        return sb.reverse().toString();
    }
}