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