405. Convert a Number to Hexadecimal

Given an integer, write an algorithm to convert it to hexadecimal. For negative integer,two’s complementmethod is used.
Note:All letters in hexadecimal (a-f) must be in lowercase.The hexadecimal string must not contain extra leading0s. 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.
Youmust not useanymethod provided by the librarywhich converts/formats the number to hex directly.
Example 1:
Input: 26  Output: "1a"
Example 2:
Input: -1   Output:  "ffffffff"

正负十进制数转成16进制数

这个要用到无符号右移，不能直接/16 否则负数会溢出。 这题真是会了不难， 不会太难的类型。