[LeetCode] C++: Simple Question-Bit Operation 405. Convert Numbers to Hexadecimal Numbers

405. Number conversion to hexadecimal number

Easy difficulty 122

Given an integer, write an algorithm to convert this number into a hexadecimal number. For negative integers, we usually use one's  complement arithmetic  .

note:

1. All letters ( a-f) in the hexadecimal system must be lowercase.
2. No extra leading zeros can be included in the hexadecimal string. If the number to be converted is 0, it '0'is represented by a single character ; in other cases, the first character in the hexadecimal string will not be a 0 character. 
3. The given number is guaranteed to be in the 32-bit signed integer range.
4. You cannot use any method provided by the library to directly convert or format a number to hexadecimal.

Example 1:

Input: 
26 

Output: 
"1a"

Example 2:

Input: 
-1 

Output: 
"ffffffff"

violence

class Solution {
public:
    string toHex(int num) {
        string res = "";
        if(num == 0){
            return "0";
        }
        vector<char> vec = {
            '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
            'a', 'b', 'c', 'd', 'e', 'f'
        };
        unsigned int n = num;
        while(n != 0){
            string tmp(1, vec[n%16]);
            res = tmp + res;
            n /= 16;
        }
        return res;
    }
};