405. 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:
All letters in hexadecimal (a-f) must be in lowercase.
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.
The given number is guaranteed to fit within the range of a 32-bit signed integer.
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：

思路：

Time Complexity: O(N) Space Complexity: O(N)

Solution Code：

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