[leetcode-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"

思路：

参考了牛人代码。位操作，将num的后4位 与 oxf 相与，这么做的好处是，不管负数还是正数都可以这样处理。

学习了。。

const string HEX = "0123456789abcdef";
class Solution {
public:
    string toHex(int num) {
        if (num == 0) return "0";
        string result;
        int count = 0;
        while (num && count++ < 8) {
            result = HEX[(num & 0xf)] + result;
            num >>= 4;
        }
        return result;
    }
};

参考：

https://discuss.leetcode.com/topic/60431/concise-c-solution