405. Convert a Number to Hexadecimal

#### QUESTION:

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”

#### SOLUTION:

``````public String toHex(int num) {
char[] numstring = Integer.toBinaryString(num).toCharArray();
StringBuilder result = new StringBuilder();
int index = numstring.length;
while(index>0){
double sum = 0;
for(int i = 0;i<4;i++){
sum = index-1>=0 ? sum+Integer.parseInt(""+numstring[index-1]) * Math.pow(2,i) : sum;
index--;
}
result.insert(0,Integer.toHexString((int)sum));
}
return result.toString();
}

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

``````