LeetCode Convert a Number to Hexadecimal 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"

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题意：把一个十进制数转换为十六进制数。如果是负数，则用补码的二进制转换为十六进制。简单题，因为计算机内存存储的就是补码，所以我们只需要取出每4bit，转换为十六进制就好。4bit对应的十六进制字符，可以提前用一个字典（或数组）存储好。 完整代码如下： [cpp] class Solution { public: string toHex(int num) { if (num == 0)return "0"; vector<string> dict = { "0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f" }; int mask = 0xf; string ans = ""; for (int i = 0; i < 8; ++i) { if (num == 0)break; ans = dict[num&mask] + ans; num >>= 4; } return ans; } }; [/cpp] 本代码提交AC，用时3MS。]]>