leetcode part1--十六进制的转换

题目： 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.

解决方法：如果单纯的推算十六进制的方法来做，需要考虑0，负数与正数的区别
但可以利用数据在计算机中的存储形式，每次读取存储的后四位，并按照0-9，a-z的形式读取即可。然后再将数据右移，重复此操作直至所有数据均读取。
public String toHex(int num) {
String s="";
do{
int rem = num & 15;
if(rem < 10)
s=rem+s;
else
{
s=(char)(rem-10+‘a’)+s;
}
num >>>= 4;
}while(num!=0);
return s;
}