Leetcode: Convert a Number to Hexadecimal

Posted 2020-08-21 neverlandly

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"

记住要delete begining 0

 1 public class Solution {
 2     public String toHex(int num) {
 3         StringBuffer res = new StringBuffer();
 4         String[] charMap = new String[]{"0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f"};
 5         for (int i=0; i<8; i++) {
 6             int number = num & (0b1111);
 7             num = num >>> 4;
 8             res.insert(0, charMap[number]);
 9         }
10         while (res.charAt(0)==‘0‘ && res.length()>1) res.deleteCharAt(0);
11         return res.toString();
12     }
13 }

 

要记住单独处理 num == 0的情况

 1 public class Solution {
 2     public String toHex(int num) {
 3         if (num == 0) return "0";
 4         StringBuffer res = new StringBuffer();
 5         String[] charMap = new String[]{"0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f"};
 6         while (num != 0) {
 7             int number = num & (0b1111);
 8             num = num >>> 4;
 9             res.insert(0, charMap[number]);
10         }
11         return res.toString();
12     }
13 }