leetcode解题: Convert a Number to Hexadecimal (405)

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iven 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”

解法1：

16进制每一位表示4个bit的信息，4个bit可以表示0到15的数字，0~9用阿拉伯数字，10~15分别用a ~ f 表示。 那么基本思路就是每一次获取最右边的4位数，然后转化为16进制的数字。然后右移直到数字变为0。
C++
要注意的是C++ 中如果用+ 操作在string 和 string上，只能char或者string，所以如果是int则要转化为char再进行操作。

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class Solution {
public:
    string toHex(int num) {
        if (num == 0) {
            return "0";
        }
        string res = "";
        
        int count = 0;
        while (num != 0 && count < 8) {
            int temp = num & 0xf;
            if (temp < 10) {
                res = to_string(temp) + res;
            } else {
                res = char('a' + temp - 10) + res;
            }
            num = num >> 4;
            ++count;
        }
        return res;
    }
};

Java

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