The Most Wanted Letter

The Most Wanted Letter

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You are given a text, which contains different English letters and punctuation symbols. You should find the most frequent letter in the text. The letter returned must be in lower case.
While checking for the most wanted letter, casing does not matter, so for the purpose of your search, "A" == "a". Make sure you do not count punctuation symbols, digits and whitespaces, only letters.


If you have two or more letters with the same frequency, then return the letter which comes first in the Latin alphabet. For example -- "one" contains "o", "n", "e" only once for each, thus we choose "e".

Input: A text for analysis as a string (str).

Output: The most frequent letter in lower case as a string (str).


assert checkio("Hello World!") == "l"
assert checkio("How do you do?") == "o"
assert checkio("One") == "e"
assert checkio("Oops!") == "o"

How it is used: For most decryption tasks you need to know the frequency of occurrence for various letters in a section of text. For example: we can easily crack a simple addition or substitution cipher if we know the frequency in which letters appear. This is interesting stuff for language experts!

A text contains only ASCII symbols.
0 < len(text) ≤ 105

Invalid hot key. Each hot key should be unique and valid
Hot keys:
CheckiO Extensions

CheckiO Extensions allow you to use local files to solve missions. More info in a blog post.

In order to install CheckiO client you'll need installed Python (version at least 3.8)

Install CheckiO Client first:

pip3 install checkio_client

Configure your tool

checkio --domain=py config --key=

Sync solutions into your local folder

checkio sync

(in beta testing) Launch local server so your browser can use it and sync solution between local file end extension on the fly. (doesn't work for safari)

checkio serv -d

Alternatevly, you can install Chrome extension or FF addon

checkio install-plugin
checkio install-plugin --ff
checkio install-plugin --chromium

Read more here about other functionality that the checkio client provides. Feel free to submit an issue in case of any difficulties.

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