leetcode_405

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"

Solutions

1. straight forward

class Solution {
public:
    string toHex(int num) {
        if (!num) return "0";
        string hex = "0123456789abcdef";
        string res;
        // the behavior of right shift of negative number is undefined.
        // ie may fill 1 at the highest bit, thus the while loop never breaks
        unsigned n = num;
        while (n) {
            res = hex[n % 16] + res;
            n /= 16;
            // res = hex[n & 0b1111] + res;
            // n >>= 4;
        }
        return res;
    }
};