[LeetCode] Problem 405 - Convert a Number to Hexadecimal

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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

No.1

Input:
26

Output:
“1a”

No.2

Input:
-1

Output:
“ffffffff”

Code

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public String toHex(int num) {
    StringBuilder sb = new StringBuilder();
    String str = "0123456789abcdef";
    int count = 0;

    while (num != 0 && count < 8) {
        char ch = str.charAt(num & 0xf);
        sb.append(ch);
        num >>= 4;
        count++;
    }

    return sb.length() == 0 ? "0" : sb.reverse().toString();
}