Is Hexspeak easy or hard?

Hexspeak is classified as an Easy problem. The core tasks are hexadecimal conversion and simple string validation. The challenge mainly comes from correctly handling the digit mapping and detecting invalid digits.

Hexspeak Python/Java solution

In Python or Java, convert the decimal string to a long integer, generate the hexadecimal representation, then iterate through the characters. Replace '0' with 'O', '1' with 'I', and allow 'A'–'F'. If any character from '2' to '9' appears, return "ERROR". The logic is identical across Python, Java, C++, and Go.

How to solve Hexspeak in O(n)?

Convert the decimal input to a hexadecimal string, then iterate through each character once. Replace '0' with 'O', '1' with 'I', keep 'A'–'F' unchanged, and reject digits '2'–'9'. Because each character is processed exactly once, the total complexity is O(n).

What is the best approach for Hexspeak?

The best approach converts the decimal string to hexadecimal and then simulates the Hexspeak transformation rules. Iterate through the hex string and map 0 → O and 1 → I while keeping A–F unchanged. If digits 2–9 appear, return ERROR. This runs in O(n) time and O(n) space.

Is Hexspeak asked at Google/Amazon/Meta?

Hexspeak is not among the most frequent interview questions at large companies, but it represents a common pattern: number base conversion followed by string validation. Variants of this pattern appear in interviews at companies like Amazon or Google when testing attention to edge cases and string manipulation.

What data structure is used in Hexspeak?

The solution primarily uses strings and simple character mapping. No complex data structures are required. The algorithm relies on iterating through the hexadecimal string and constructing a new result string.

What is the time complexity of Hexspeak?

The optimal solution runs in O(n) time where n is the number of characters in the hexadecimal representation. The algorithm converts the number to hex and scans the result once for validation and character replacement. Space complexity is O(n) for storing the output string.

Description Hints 3 Solution Video 10:48

1271. Hexspeak

Easy57.5% acceptance1 companyPremium elsewhere, free here

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 <= num.length <= 12
num does not contain leading zeros.
num represents an integer in the range [1, 10¹²].

Asked at 1 company

Virtu Financial

Topics

Math String

Hints open one at a time

Hint 1

Convert the given number to hexadecimal.

Hint 2

Replace all 0 and 1 with 'O' and 'I'.

Hint 3

Check if the final string has any numerical digits.

10:48

Still stuck?Read the written solution, or watch a walkthrough.

Open solution

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1class Solution:
  def solve(self):
      pass


Starter codePython 3Spaces: 4

Examples

Case 1Case 2

Input

"257"

Input

"3"

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