Description

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"

My solution

很自然的想到>>4bit方式, &0xf相当于对16取余, 用unordered_map把11,12,13,14,15转为abcdef, 但是细节处理仍有待进步, 具体参见下文discuss优秀答案(基本原理一致).

class Solution {public:    string toHex(int num) {        if (num == 0) return "0";        string res;        unordered_map
    
      mp;        mp[10] = 'a';        mp[11] = 'b';        mp[12] = 'c';        mp[13] = 'd';        mp[14] = 'e';        mp[15] = 'f';        int last, cnt = 0;        while (num && ++cnt <= 8) {            last = num & 0xf;            res = last > 9 ? mp[last] + res : to_string(last) + res;            num >>= 4;        }        return res;    }};
    

Discuss

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;    }};

Reference