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## Problem

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"


## Code

Two’s complement 补码

>> arithmetic shift
>>> logic shift


-2 的结果

11111111111111111111111111111110
1111111111111111111111111111
111111111111111111111111
11111111111111111111
1111111111111111
111111111111
11111111
1111
0

class Solution {
public String toHex(int num) {
char[] map = new char[]{'0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f'};
if(num == 0) return "0";

String res = "";
while(num != 0){
res= map[num & 15] + res;
num = (num >>> 4);
}

return res;
}
}