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:

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"

思路：将一个整数转换成十六进制表示的字符串。整数在计算机内部以补码表示，对于正数，直接每次取出它的后4位表示的数，可以将它和0xF相与，也可以对16取模，取完右移四位。知道数被移位成0。尤其注意负数的情况，有符号整数在C++中右移时，用符号位补足前面的位。所以，负数怎么移位它还是负数。那么就将负数处理成无符号整数，注意代码中的处理。

38. leetcode 405. Convert a Number to Hexadecimal