> For the complete documentation index, see [llms.txt](https://jaywin.gitbook.io/leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jaywin.gitbook.io/leetcode/solutions/1271-hexspeak.md).

# 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.

## ac

```java
```