405. 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:

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:26Output:"1a"

Example 2:

Input:-1Output:"ffffffff"

10进制转化2进制，每四位一个组合，如果是0，返回‘0’。代码如下：

public class Solution {    char[] ch = {'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";        }        StringBuilder result = new StringBuilder();        while (num != 0) {            result.insert(0, ch[num & 15]);            num = num >>> 4;        }        return result.toString();    }}