405. Convert a Number to Hexadecimal

原题网址：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:

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"

方法：通过二进制转换。

public class Solution {    private char[] hex(int num) {        char[] hex = new char[8];        for(int i = 7; i >= 0; i--) {            hex[i] = (num & 0b1111) < 10 ? (char)('0' + (num & 0b1111)) : (char)('a' + (num & 0b1111) - 10);            num >>>= 4;        }        return hex;    }    public String toHex(int num) {        char[] hex = hex(num);        StringBuilder sb = new StringBuilder();        boolean nonzero = false;        for(int i = 0; i < hex.length; i++) {            if (hex[i] != '0') {                nonzero = true;            }            if (nonzero) {                sb.append(hex[i]);            }        }        if (sb.length() == 0) {            sb.append('0');        }        return sb.toString();    }}