405. Convert a Number to Hexadecimal

原題網址：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:
26

Output:
"1a"

Example 2:

Input:
-1

Output:
"ffffffff"

方法：通過二進制轉換。

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();
    }
}