Python Coding Challenges

strings parsing run-length-encoding

Expand compressed string

Implement a function that expands run-length encoded strings (e.g., 'a3b2' → 'aaabb').

Find substring index

Implement a function that returns the starting index of the first occurrence of a substring using only basic string indexing and slicing.

string search index

strings counting substrings

Count Substrings

Implement a function that counts non-overlapping occurrences of a substring in a given string.

Sort characters in string

Write a function that sorts the characters in a string and returns the sorted string.

sorting string character

Index of First Occurrence

Implement a function that finds the starting index of a substring within a string, returning -1 when absent.

strings search index

formatting strings function

Error message formatter

Write a function that constructs a formatted error message from a code, an optional context, and a fallback message.

Stack Trace Sanitizer

Implement a function that rewrites traceback file paths to basenames only.

strings regex parsing

string-parsing split strip

Parse Log Line

Write a function that parses a log line and returns a dictionary with timestamp, level, and message.

strings whitespace normalization

Replace multiple spaces

Implement a function that replaces every sequence of spaces with a single space.

Extract Quoted Strings

Write a function that extracts the text inside every double-quoted substring from a given string.

strings parsing quotes

strings whitespace split-join

Normalize Whitespace

Write a function that normalizes any whitespace in a string to single spaces and trims the ends.

+5 pts 10m

Strip Leading Zeros

Write a function that strips leading zeros from a string representing a non-negative integer.

strings strip lstrip

+5 pts 5m

Find all numbers in text

Write a function that extracts all standalone integers from a text string using regular expressions.

regex parsing numbers

strings parsing file-paths

Extract file extensions

Implement a function that extracts the extension from a filename according to standard rules.

strings validation returns

Validate username format

Implement a function that validates a username according to length, allowed characters, and no consecutive underscores.

string-manipulation parsing template

Replace template variables

Implement a function that replaces {{variable}} placeholders in a string using a dictionary, leaving unknown placeholders intact.

strings character-comparison distance

Hamming Distance

Implement a function that computes the Hamming distance between two strings of equal length.

Caesar Cipher Decrypt

Implement a function that decrypts a Caesar cipher by shifting letters back by a given number.

strings ascii cipher

Strings & Text medium

Simplify Path

Implement a function that simplifies a Unix-style absolute file path to its canonical form.

strings stack parsing

+20 pts 25m

strings deduplication order-preserving

Remove Duplicate Letters

Implement a function that removes duplicate characters from a string while preserving the order of their first occurrence.

Strings & Text medium

Change directory manager

Implement a function that processes `cd` commands and returns the resulting absolute path.

string parsing paths

+20 pts 20m

Parse HTTP Status Line

Write a function that parses a well-formed HTTP status line into its three components.

strings parsing http

+8 pts 15m

Parse markdown headers

Write a function that parses markdown headers and returns their levels and texts.

markdown parsing strings

Decode base64 string

Write a function that decodes a base64 string to its original UTF-8 text without using the base64 module.

base64 decode strings