LeetCode 405. Convert a Number to Hexadecimal

题目描述:

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"

由于传入的数据是int型, 所以其实负数就已经是用补码来表示了. 因此只要每次取四位二进制位出来然后把它们转换为16进制即可.

class Solution {
public:
    string toHex(int num) {
        int n = num;
        string hex;
        for(int i = 0; i < 8; i++){
            hex.push_back(toCharHex(n & 0xf));
            n >>= 4;
        }
        while(hex.size() > 1 && hex.back() == '0') hex.pop_back();
        reverse(hex.begin(), hex.end());
        return hex;
    }
    
    char toCharHex(int num){
        if(num < 10){
            return num + '0';
        }
        else{
            return num - 10 + 'a';
        }
    }
};