405. Convert a Number to Hexadecimal

Posted 2020-09-07 为了更优秀的你，加油！

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"

class Solution {
public:
    string toHex(int num) {
        char ma[]={‘0‘,‘1‘,‘2‘,‘3‘,‘4‘,‘5‘,‘6‘,‘7‘,‘8‘,‘9‘,‘a‘,‘b‘,‘c‘,‘d‘,‘e‘,‘f‘};
        string ans="";
        do{
            ans=ma[num & 15]+ans; //四位二进制转化成一个十六进制
            num>>=4;    //每次处理四位
        }while(num&&ans.size()<8);
        return ans;
    }
};