十进制转十六进制

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

每4个bit作为一个单位，处理起来思路更直接

Java

class Solution {
    public String toHex(int num) {
        String hexStr = "0123456789abcdef", rlt = "";
        int cnt = 0;
        while(num != 0 && cnt++ < 8) {
            rlt = hexStr.charAt(num & 0xf) + rlt;
            num >>= 4;
        }
        return rlt.isEmpty() ? "0" : rlt;
    }
}