Convert a Number to Hexadecimal问题及解法

问题描述：

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 (de >a-fde>) must be in lowercase.
2. The hexadecimal string must not contain extra leading de >0de>s. If the number is zero, it is represented by a single zero character de >'0'de>; 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.

示例：

Example 1:

Input:26Output:"1a"

Example 2:

Input:-1Output:"ffffffff"

问题分析：

只需要求解出每四位对应的16进制数即可，这里有个小技巧，在num移位过程中，注意保持num始终大于0.

过程详见代码：

class Solution {public:    string toHex(int num) {        char hex[16] = {'0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f'};    string res = "";        if(num == 0) return "0";int bit4 = 15;for(int i = 0; i < 8 && num; i++){int temp = bit4 & num;res.insert(res.begin(),hex[temp]);num >>= 4;}return res;    }};