38. leetcode 405. Convert a Number to Hexadecimal

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"

分析：将一个整数的二进制补码表示转化成对应十六进制的表示形式。正整数的补码就是它本身的原码表示，负整数的补码为它对应的正数的原码取反后加1。得到最终的二进制补码后，每次取出它的后4位表示的数，可以通过将它和0xF相与，也可以将它对16取模，取完右移四位，直到原数被被移位为0。