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"
   

The trick of this problem is to use bitwise “AND” in java and unsigned right bit-shift operator in Java (“>>>”)

Basic idea: each time take a look at the last four digits of binary verion of the input, and maps that to a hex char shift the input to the right by 4 bits, do it again until input becomes 0.

class Solution {
    public String toHex(int num) {
        String res="";
        char[] map = {'0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f'};
        if(num==0) return "0";
        while(num!=0){
            res = map[num&15]+res;
            num = num>>>4;
        }
        return res;
    }
}

summarize of Java primitive data types:

1. byte: Byte data type is a 8-bit signed two’s complement integer.
2. Short: Short data type is a 16-bit signed two’s complement integer.
3. int: Int data type is a 32-bit signed two’s complement integer.
4. long: Long data type is a 64-bit signed two’s complement integer.
5. float: Float data type is a single-precision 32-bit IEEE 754 floating point.
6. double: double data type is a double-precision 64-bit IEEE 754 floating point.
7. boolean: boolean data type represents one bit of information.
8. char: char data type is a single 16-bit Unicode character.

Two’s complement

“The good example is from wiki that the relationship to two’s complement is realized by noting that:
256 = 255 + 1, and (255 − x) is the ones’ complement of x

(0111=7)

two's complement is:
```1111 1001= -7

Source