405.十进制转换成十六进制 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"

public class Solution {
    public string ToHex(int num) {
        if (num == 0)
        {
            return "0";
        }
        long number = Convert.ToInt64(num);
        if (number < 0)
        {
            number = UInt32.MaxValue + number + 1;//取反+1
        }
        char[] hex = { ‘0‘, ‘1‘, ‘2‘, ‘3‘, ‘4‘, ‘5‘, ‘6‘, ‘7‘, ‘8‘, ‘9‘, ‘a‘, ‘b‘, ‘c‘, ‘d‘, ‘e‘, ‘f‘ };
        string hexString = "";
        long n = 0;
        char c = ‘ ‘;
        while (number > 0)
        {
            n = number % 16;
            c = hex[n];
            hexString = c + hexString;
            number /= 16;
        }
        return hexString;
    }
}