1271. Hexspeak

https://leetcode.com/problems/hexspeak

Description

A decimal number can be converted to its Hexspeak representation by first converting it to an uppercase hexadecimal string, then replacing all occurrences of the digit 0 with the letter O, and the digit 1 with the letter I. Such a representation is valid if and only if it consists only of the letters in the set {"A", "B", "C", "D", "E", "F", "I", "O"}.

Given a string num representing a decimal integer N, return the Hexspeak representation of N if it is valid, otherwise return "ERROR".

Example 1:

**Input:** num = "257"
**Output:** "IOI"
**Explanation:**  257 is 101 in hexadecimal.

Example 2:

**Input:** num = "3"
**Output:** "ERROR"

Constraints:

• 1 <= N <= 10^12

• There are no leading zeros in the given string.

• All answers must be in uppercase letters.

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