Python String Exercises: 35+ Coding Problems with Solutions

As you know, strings are widely used to store textual data. To perform programming tasks in Python, a good understanding of string manipulation is essential.

This article provides 35+ Python String practice questions that focus entirely on string operations, manipulation, slicing, and string functions.

Each coding challenge includes a Practice Problem, Hint, Solution code, and detailed Explanation, ensuring you don’t just copy code, but genuinely practice and understand how and why it works.

• All solutions have been fully tested on Python 3.
• Interactive Learning: Use our Online Code Editor to solve these exercises in real time.

Let us know if you have any alternative solutions. It will help other developers.

Exercise 1. Create a string made of the first, middle, and last character

Practice Problem: Write a program to create a new string made of an input string’s first, middle, and last characters.

Exercise Purpose: This exercise teaches the fundamentals of String Indexing. Accessing specific positions, especially the middle that requires calculating length, is a foundational skill for data parsing and text manipulation.

Given Input: str1 = "James"

Expected Output: Jms

str1 = "James"
print("Original String is", str1)

# Get first character
first_char = str1[0]

# Get middle character
# Calculate index by dividing length by 2
res = len(str1)
middle_index = int(res / 2)
mid_char = str1[middle_index]

# Get last character
last_char = str1[-1]

# Combine characters
res_str = first_char + mid_char + last_char
print("New String:", res_str)Code language: Python (python)

Exercise 2. Create a string made of the middle three characters

Practice Problem: Write a program to create a new string made of the middle three characters of an input string of odd length.

Exercise Purpose: This builds on indexing by introducing String Slicing. Slicing is a powerful Python feature that lets you extract entire “chunks” of data efficiently.

Given Input: str1 = "JhonDipPeta"

Expected Output: Dip

def get_middle_three_chars(str1):
    print("Original String is", str1)

    # Find middle index
    mi = int(len(str1) / 2)

    # Slice string from (mid - 1) to (mid + 2)
    res = str1[mi - 1:mi + 2]
    print("Middle three chars are:", res)

get_middle_three_chars("JhonDipPeta")
get_middle_three_chars("JaSon")Code language: Python (python)

Exercise 3. Append new string in the middle of a given string

Practice Problem: Given two strings, s1 and s2, create a new string by appending s2 in the middle of s1.

Exercise Purpose: This exercise introduces String Partitioning and Concatenation. In programming, you often need to “inject” data into a template or modify strings at specific locations.

Given Input: s1 = "Ault" s2 = "Kelly"

Expected Output: AuKellylt

def append_middle(s1, s2):
    print("Original Strings are", s1, s2)

    # Find middle index of first string
    mi = int(len(s1) / 2)

    # Get character from 0 to middle index
    x = s1[:mi]
    # Get character from middle index to end
    y = s1[mi:]

    # Combine all three
    res = x + s2 + y
    print("After appending new string in middle:", res)

append_middle("Ault", "Kelly")Code language: Python (python)

Exercise 4. Create a new string made of the first, middle, and last characters of each input string

Practice Problem: Given two strings, s1 and s2, create a new string from the first, middle, and last characters of each input string.

Exercise Purpose: This exercise practices Complex Concatenation. It requires multiple independent extractions and organizing them into a single result, common when generating IDs or codes from user data.

Given Input: s1 = "America" s2 = "Japan"

Expected Output: AJrpan

s1 = "America"
s2 = "Japan"

# Get first, middle and last character from first string
first_char = s1[0]
middle_char = s1[int(len(s1) / 2)]
last_char = s1[-1]

# Get first, middle and last character from second string
first_char2 = s2[0]
middle_char2 = s2[int(len(s2) / 2)]
last_char2 = s2[-1]

# Combine all
res = first_char + first_char2 + middle_char + middle_char2 + last_char + last_char2
print("New String:", res)Code language: Python (python)

Exercise 5. Reverse a given string

Practice Problem: Write a program to reverse a given string.

Exercise Purpose: Reversing a string is a classic logic-building exercise. In Python, this is most efficiently done via Slicing, demonstrating the language’s ability to manipulate sequences using “steps.” It is a prerequisite for solving problems like palindrome detection.

Given Input: str1 = "PYnative"

Expected Output: evitanYP

str1 = "PYnative"
print("Original String is:", str1)

# Using string slicing
# The -1 step starts from the end and moves toward the beginning
str1 = str1[::-1]

print("Reversed String is:", str1)Code language: Python (python)

Exercise 6. Find the last position of a given substring

Practice Problem: Write a program to find the last index of the substring “Emma” in a given string.

Exercise Purpose: While the .find() method searches from the beginning of a string, the .rfind() method (Reverse Find) locates the most recent occurrence of a specified pattern. This functionality is essential when parsing file paths or URLs that require identification of the final delimiter.

Given Input: str1 = "Emma is a data scientist who knows Python. Emma works at google."

Expected Output: Last occurrence of Emma starts at index 43

str1 = "Emma is a data scientist who knows Python. Emma works at google."
print("Original String is:", str1)

# Find the last occurrence of "Emma"
last_index = str1.rfind("Emma")

print("Last occurrence of Emma starts at index:", last_index)Code language: Python (python)

Exercise 7. Split a string on hyphens

Practice Problem: Write a program to split a given string on hyphens and display each substring.

Exercise Purpose: This exercise introduces the concept of tokenization. Dividing strings into smaller components based on delimiters, such as commas, spaces, or hyphens, is a common technique for processing CSV files, logs, and user-entered lists.

Given Input: str1 = "Emma-is-a-data-scientist"

Expected Output:

Displaying each substring: 
Emma
is
a
data
scientist

str1 = "Emma-is-a-data-scientist"
print("Original String is:", str1)

# split string
sub_strings = str1.split("-")

print("Displaying each substring")
for s in sub_strings:
    print(s)Code language: Python (python)

Exercise 8. Find all occurrences of a substring in a given string by ignoring the case

Practice Problem: Write a program to find the total count of the substring “USA” in a given string, ignoring the case (i.e., both “usa” and “USA” should be counted).

Exercise Purpose: This exercise addresses case normalization. In practical data science and web scraping applications, text data is frequently inconsistent. Converting all text to lowercase prior to processing is considered a standard best practice.

Given Input: str1 = "Welcome to USA. usa awesome, isn't it?"

Expected Output: The USA count is: 2

str1 = "Welcome to USA. usa awesome, isn't it?"
sub_string = "USA"

# convert both to lower case
temp_str = str1.lower()
count = temp_str.count(sub_string.lower())

print("The USA count is:", count)Code language: Python (python)

Exercise 9. String characters balance test

Practice Problem: Write a program to check if two strings are balanced. For example, strings s1 and s2 are balanced if all the characters in s1 are present in s2. The character’s position doesn’t matter.

Exercise Purpose: This exercise focuses on membership testing. This fundamental concept is utilized in data validation, such as verifying whether a password contains required characters or determining if a search query matches a database entry.

Given Input:

Case 1: s1 = "yn", s2 = "PyNative"
Case 2: s1 = "ynf", s2 = "PyNative"

Expected Output:

Case 1: True
Case 2: False

def string_balance_check(s1, s2):
    flag = True
    for char in s1:
        if char in s2:
            continue
        else:
            flag = False
            break
    return flag

s1 = "yn"
s2 = "PyNative"
print("Is s1 and s2 balanced:", string_balance_check(s1, s2))

s1 = "ynf"
s2 = "PyNative"
print("Is s1 and s2 balanced:", string_balance_check(s1, s2))Code language: Python (python)

Exercise 10. Vowel Counter

Practice Problem: Write a program to count the total number of vowels (a, e, i, o, u) in a given string.

Given Input: str1 = "Hello World"

Expected Output: Vowel Count: 3

str1 = "Hello World"
vowels = "aeiouAEIOU"
count = 0

for char in str1:
    if char in vowels:
        count += 1

print("Vowel Count:", count)Code language: Python (python)

Exercise 11. Prefix/Suffix Check

Practice Problem: Check if a given URL starts with “https” and ends with “.com”.

Exercise Purpose: This exercise teaches Boolean Validation. Methods like .startswith() and .endswith() are cleaner and less error-prone than manual slicing for verifying file formats, protocols, or naming conventions.

Given Input: str1 = "https://google.com"

Expected Output: Is valid URL: True

str1 = "https://google.com"

# Check both start and end conditions
is_secure = str1.startswith("https")
is_com = str1.endswith(".com")

if is_secure and is_com:
    print("Is valid URL: True")
else:
    print("Is valid URL: False")Code language: Python (python)

Exercise 12. Swap Case

Practice Problem: Write a program to toggle the case of all characters in a string (uppercase becomes lowercase and vice versa).

Exercise Purpose: This demonstrates Case Transformation. Though simple, it is often used in search algorithms to normalize data or in text editors to provide “Toggle Case” functionality.

Given Input: str1 = "PyThOn"

Expected Output: pYtHoN

str1 = "PyThOn"

# Swap all cases
res = str1.swapcase()

print("Original:", str1)
print("Swapped :", res)Code language: Python (python)

Exercise 13. Remove Whitespace

Practice Problem: Remove every single space from a given string, including spaces between words.

Exercise Purpose: This highlights the difference between Trimming and Filtering. While .strip() only removes leading/trailing spaces, .replace() can reach inside a string to remove characters globally.

Given Input: str1 = " P y t h o n "

Expected Output: Python

str1 = " P y t h o n "

# Replace space with nothing
res = str1.replace(" ", "")

print("Cleaned string:", res)Code language: Python (python)

Exercise 14. N-th Character Removal

Practice Problem: Write a program to remove the character at index i from a string.

Exercise Purpose: Since Python strings are Immutable (you can’t just delete a character at an index), this exercise teaches you how to “reconstruct” a string by skipping over a specific part.

Given Input: str1 = "Python", i = 2

Expected Output:

Pyhon (The character 't' at index 2 was removed)

str1 = "Python"
i = 2

# Slice from start to i (exclusive)
first_part = str1[:i]

# Slice from i+1 to the end
last_part = str1[i+1:]

# Combine
res = first_part + last_part

print("After removing index", i, ":", res)Code language: Python (python)

Exercise 15. String Partitioning

Practice Problem: Use the .partition() method to split a string into three parts: the part before a separator, the separator itself, and the part after it.

Exercise Purpose: .split() is great for breaking a string into many pieces. .partition() is a specialized tool that always returns a 3-tuple. It is especially useful for parsing data like email addresses or key-value pairs where the separator needs to be preserved or accounted for.

Given Input: str1 = "username@company.com", sep = "@"

Expected Output: ('username', '@', 'company.com')

str1 = "username@company.com"

# Partition the string at the first '@'
res = str1.partition("@")

print("Original String:", str1)
print("Partitioned Result:", res)
# Accessing specific parts
print("Username:", res[0])Code language: Python (python)

Exercise 16. Extract File Extension

Practice Problem: Given a filename as a string, extract only the file extension (e.g., .png or .pdf).

Exercise Purpose: This exercise teaches String Parsing. In software development, you need to validate file types before processing uploads. It helps you practice finding the last occurrence of a character (the dot) to handle files with multiple dots correctly (like archive.tar.gz).

Given Input: file_name = "report_final_v2.pdf"

Expected Output: pdf

file_name = "report_final_v2.pdf"

# Method 1: Using split and taking the last item
extension = file_name.split(".")[-1]

print("File Name:", file_name)
print("Extension:", extension)Code language: Python (python)

Exercise 17. Lowercase First

Practice Problem: Write a program to arrange string characters such that all lowercase letters come first, followed by all uppercase letters.

Exercise Purpose: This exercise introduces Conditional Filtering and Reassembly. It’s a common pattern in data sorting: you need to group items by a specific property (in this case, “casing”) while preserving their relative order.

Given Input: str1 = "PyNaTive"

Expected Output: yaivePNT

str1 = "PyNaTive"
lower = []
upper = []

for char in str1:
    if char.islower():
        lower.append(char)
    else:
        upper.append(char)

# Join both lists
res = "".join(lower + upper)
print("Result:", res)Code language: Python (python)

Exercise 18. Count all letters, digits, and special symbols from a given string

Practice Problem: Write a program to count all letters, digits, and special symbols from a given string.

Exercise Purpose: This introduces Character Classification. Using built-in string methods like .isalpha() and .isdigit() is the standard way to validate user input and perform data cleaning.

Given Input: str1 = "P@#yn26at^&i5ve"

Expected Output:

Total counts of chars, digits, and symbols: Chars = 8 Digits = 3 Symbol = 4

def count_chars_digits_symbols(sample_str):
    char_count = 0
    digit_count = 0
    symbol_count = 0
    for char in sample_str:
        if char.isalpha():
            char_count += 1
        elif char.isdigit():
            digit_count += 1
        # if it is not letter or digit then it is a special symbol
        else:
            symbol_count += 1

    print("Chars =", char_count, "Digits =", digit_count, "Symbol =", symbol_count)

sample_str = "P@#yn26at^&i5ve"
print("total counts of chars, digits, and symbols")
count_chars_digits_symbols(sample_str)Code language: Python (python)

Exercise 19. Create a mixed string using alternating characters

Practice Problem: Given two strings, s1 and s2, create a third string made of the first char of s1, then the last char of s2, Next, the second char of s1 and the second-to-last char of s2, and so on. Any left-over chars go at the end of the result.

Exercise Purpose: This exercise sharpens your ability to handle Multiple Pointer Traversal. It makes you think about coordinating indices moving in opposite directions (forward through one string and backward through another).

Given Input: s1 = "Abc" s2 = "Xyz"

Expected Output: AzbycX

s1 = "Abc"
s2 = "Xyz"

# Get string length
s1_length = len(s1)
s2_length = len(s2)

# Use length of the bigger string
length = s1_length if s1_length > s2_length else s2_length
result = ""

# Reverse s2 to make it easier to pick characters from the end
s2 = s2[::-1]

# Iterate through the range
for i in range(length):
    if i < s1_length:
        result = result + s1[i]
    if i < s2_length:
        result = result + s2[i]

print(result)Code language: Python (python)

Exercise 20. Calculate the sum and average of the digits present in a string

Practice Problem: Given a string, run a loop to calculate the sum and average of the digits that appear in the string. Ignore all other characters.

Exercise Purpose: This combines Data Extraction with Arithmetic Operations. It demonstrates how to filter relevant data (numbers) out of a “noisy” string (letters and symbols) to perform calculations.

Given Input: str1 = "PYnative29@#8496"

Expected Output: Sum is: 38 Average is 6.33

str1 = "PYnative29@#8496"
total_sum = 0
cnt = 0

for char in str1:
    if char.isdigit():
        total_sum += int(char)
        cnt += 1

# average = sum / count of digits
avg = total_sum / cnt

print("Sum is:", total_sum, "Average is", avg)Code language: Python (python)

Exercise 21. Count occurrences of all characters within a string

Practice Problem: Count the frequency of every character in a string and store the results in a dictionary.

Exercise Purpose: This exercise introduces Frequency Mapping using Dictionaries. Dictionaries are essential for counting and organizing data because they store unique “keys” (the characters) and associated “values” (their counts).

Given Input: str1 = "apple"

Expected Output: {'a': 1, 'p': 2, 'l': 1, 'e': 1}

str1 = "apple"

# Create an empty dictionary
char_dict = dict()

for char in str1:
    # Check if character is already in the dictionary
    if char in char_dict:
        char_dict[char] += 1
    else:
        # Add the character to the dictionary
        char_dict[char] = 1

print(char_dict)Code language: Python (python)

Exercise 22. Remove empty strings from a list of strings

Practice Problem: Given a list of strings, remove any empty strings or None values from it.

Exercise Purpose: This introduces Data Cleaning. Real-world datasets often have missing or empty values. Learning to filter lists is essential to prevent your program from crashing when processing empty data points.

Given Input: str_list = ["Emma", "Jon", "", "Kelly", None, "Eric", ""]

Expected Output: ['Emma', 'Jon', 'Kelly', 'Eric']

str_list = ["Emma", "Jon", "", "Kelly", None, "Eric", ""]
print("Original list of strings:", str_list)

# use filter() to remove None and empty strings
# filter(None, sequence) removes all falsy values
new_str_list = list(filter(None, str_list))

print("After removing empty strings:", new_str_list)Code language: Python (python)

Exercise 23. Remove special symbols/punctuation from a string

Practice Problem: Write a program to remove all special symbols and punctuation from a given string.

Exercise Purpose: This exercise is a staple of Natural Language Processing (NLP). Before analyzing text like sentiment analysis, you must remove “noise” such as symbols and punctuation so the computer can focus on the words.

Given Input: str1 = "/*Jon is @developer & musician!!"

Expected Output: "Jon is developer musician"

import string

str1 = "/*Jon is @developer & musician!!"
print("Original string is:", str1)

# Solution 1: Using a loop and isalnum()
new_str = ""
for char in str1:
    # Keep characters if they are letters/numbers or a space
    if char.isalnum() or char.isspace():
        new_str += char

print("New string is:", new_str)Code language: Python (python)

Exercise 24. Remove all characters from a string except integers

Practice Problem: Write a program to extract only the numeric digits from a mixed string and combine them into a single string.

Exercise Purpose: This is a core part of Data Extraction. Often when scraping web data or reading OCR text from images, you get strings like “Price: $25.00”. This exercise teaches you how to strip away the “noise” such as currency, labels, and spaces to get the raw numerical data for calculations.

Given Input: str1 = "I am 25 years and 10 months old"

Expected Output: 2510

str1 = "I am 25 years and 10 months old"
print("Original string is:", str1)

# Joining only the digits found in the string
res = "".join([item for item in str1 if item.isdigit()])

print("Resulting digits:", res)Code language: Python (python)

Exercise 25. Find words with both letters and numbers

Practice Problem: Write a program to find and print words from a string that contain both letters and numbers.

Exercise Purpose: This exercise focuses on Contextual Filtering. In cybersecurity or system administration, you often need to find “alphanumeric” strings like Product IDs (e.g., PROD123), license keys, or mixed-character usernames. It teaches you how to look for specific patterns within individual tokens.

Given Input: str1 = "Emma25 is Data scientist50 and AI Expert"

Expected Output:

Emma25
scientist50

str1 = "Emma25 is Data scientist50 and AI Expert"
print("The original string is:", str1)

# Split string into individual words
res = []
temp = str1.split()

# Check each word
for item in temp:
    if any(char.isalpha() for char in item) and any(char.isdigit() for char in item):
        res.append(item)

print("Words with alphabets and numbers:")
for i in res:
    print(i)Code language: Python (python)

Exercise 26. Replace each special symbol with # in the following string

Practice Problem: Write a program to replace every special symbol (punctuation) in a string with a specific character, like #.

Exercise Purpose: Vital for Data Sanitization. Before sending text to certain databases or file systems that can’t handle symbols like @ or &, you often need to “mask” them. It’s also a great introduction to the string module’s built-in constants.

Given Input: str1 = "/*Jon is @developer & musician!!"

Expected Output: ##Jon is #developer # musician##

import string

str1 = "/*Jon is @developer & musician!!"
print("Original string is:", str1)

# Set the replacement character
replace_char = '#'

# Create a list of all punctuation symbols
punctuation = string.punctuation

for char in punctuation:
    str1 = str1.replace(char, replace_char)

print("The strings after replacement:", str1)Code language: Python (python)

Exercise 27. Palindrome Check

Practice Problem: Write a program to check if a string is a palindrome (reads the same forward and backward).

Exercise Purpose: The palindrome check is the “Hello World” of Algorithmic Logic. It teaches you how to compare a sequence against its own reflection. In real-world applications, this concept is used in DNA sequencing and data integrity verification.

Given Input: str1 = "radar"

Expected Output: Is Palindrome: True

def is_palindrome(s):
    # Normalize to lowercase to avoid case issues
    s = s.lower()
    # Compare string with its reverse
    return s == s[::-1]

print("Is 'radar' a palindrome?", is_palindrome("radar"))
print("Is 'Python' a palindrome?", is_palindrome("Python"))Code language: Python (python)

Exercise 28. Anagram Detector

Practice Problem: Write a program to check if two strings are anagrams (formed by rearranging the letters of another, such as “listen” and “silent”).

Exercise Purpose: This exercise teaches Canonical Forms. By sorting two different strings into a “standard” order (alphabetical), you can easily determine if they contain the exact same ingredients. This is a fundamental concept in data deduplication.

Given Input: s1 = "listen", s2 = "silent"

Expected Output: Are Anagrams: True

def check_anagram(s1, s2):
    # Sort both strings
    # sorted() returns a list of characters in alphabetical order
    return sorted(s1.lower()) == sorted(s2.lower())

s1 = "listen"
s2 = "silent"

if check_anagram(s1, s2):
    print(f"{s1} and {s2} are anagrams.")
else:
    print(f"{s1} and {s2} are NOT anagrams.")Code language: Python (python)

Exercise 29. Unique Character Check

Practice Problem: Write a function to determine if a string has all unique characters. Return True if every character appears only once, otherwise return False.

Exercise Purpose: This introduces the concept of Sets. In Python, a set is an unordered collection that cannot contain duplicate items. Comparing the length of a string to the length of its “set version” is the most efficient way to check for uniqueness in O(n) time.

Given Input: str1 = "python"

str2 = "alphabet"

Expected Output:

"python" unique: True
"alphabet" unique: False

def is_unique(s):
    # A set only keeps unique elements
    char_set = set(s)
    return len(char_set) == len(s)

str1 = "python"
str2 = "alphabet"

print(f"'{str1}' unique: {is_unique(str1)}")
print(f"'{str2}' unique: {is_unique(str2)}")Code language: Python (python)

Exercise 30. Title Case Logic

Practice Problem: Write a program to capitalize the first letter of every word in a sentence without using the built-in .title() method.

Exercise Purpose: This practice covers String Splitting and Indexing. While .title() exists, manually implementing it helps you understand how to isolate parts of a string, modify them, and rebuild the sentence. This is a common requirement in data transformation.

Given Input: str1 = "hello world from python"

Expected Output: Hello World From Python

str1 = "hello world from python"

# Split into words
words = str1.split()
result_words = []

for word in words:
    # Capitalize first char and add the rest
    capitalized = word[0].upper() + word[1:]
    result_words.append(capitalized)

# Join back into a sentence
res = " ".join(result_words)
print(res)Code language: Python (python)

Exercise 31. Remove Duplicate Characters

Practice Problem: Write a program to remove all duplicate characters from a string while keeping the remaining characters in their original order.

Exercise Purpose: This focuses on Order-Preserving Filtering. While a set() removes duplicates, it also ruins the order. This exercise teaches you how to use a loop and a “seen” tracker to clean data without scrambling it.

Given Input: str1 = "google"

Expected Output: gole

str1 = "google"
seen = set()
result = []

for char in str1:
    if char not in seen:
        result.append(char)
        seen.add(char)

res_str = "".join(result)
print("Original:", str1)
print("Cleaned :", res_str)Code language: Python (python)

Exercise 32. Word Reversal

Practice Problem: Reverse the order of words in a given sentence, but keep the characters within the words in their original order.

Exercise Purpose: This clarifies the difference between Sequence Reversal and Character Reversal. It’s a standard interview question that tests your ability to manipulate lists of strings rather than just raw text.

Given Input: str1 = "Python is fun"

Expected Output: fun is Python

str1 = "Python is fun"

# 1. Split into list: ['Python', 'is', 'fun']
words = str1.split()

# 2. Reverse the list: ['fun', 'is', 'Python']
reversed_words = words[::-1]

# 3. Join back into a string
res = " ".join(reversed_words)

print(res)Code language: Python (python)

Exercise 33. Character Interleaving

Practice Problem: Given two strings of equal length, merge them by alternating characters.

Exercise Purpose: This exercise introduces Parallel Iteration. In data science, you often need to merge two separate arrays of data (like names and IDs) into a single paired format. It teaches you how to coordinate multiple indices simultaneously.

Given Input: s1 = "ABC", s2 = "xyz"

Expected Output: AxByCz

s1 = "ABC"
s2 = "xyz"
res = ""

for i in range(len(s1)):
    res = res + s1[i] + s2[i]

print("Interleaved string:", res)Code language: Python (python)

Exercise 34. Longest Word

Practice Problem: Write a program to find the longest word in a given sentence. If there is a tie, return the first one found.

Exercise Purpose: This exercise practices Comparison Logic and State Tracking. It’s a fundamental pattern in programming: iterating through a collection while keeping track of the “best” (or longest/largest) item found so far.

Given Input: str1 = "The quick brown fox jumps over the lazy dog"

Expected Output: Longest word: quick

Note: “brown” and “jumps” are also 5 letters, but “quick” appears first.

str1 = "The quick brown fox jumps over the lazy dog"

# Split string into a list of words
words = str1.split()
longest = ""

for word in words:
    # If current word is strictly longer than our record, update it
    if len(word) > len(longest):
        longest = word

print("Longest word:", longest)Code language: Python (python)

Exercise 35. Acronym Creator

Practice Problem: Write a program to generate an acronym from a given phrase (e.g., “Random Access Memory” becomes “RAM”).

Exercise Purpose: This exercise focuses on String Transformation. It teaches you how to extract specific metadata (the first letter) from tokens and combine them into a new, condensed format.

Given Input: str1 = "Random Access Memory"

Expected Output: RAM

str1 = "Random Access Memory"

# Extract the first character of each word and uppercase it
acronym = "".join([word[0].upper() for word in str1.split()])

print("Acronym:", acronym)Code language: Python (python)

Exercise 36. Word Frequency

Practice Problem: Count the occurrences of each word in a string and store the result in a dictionary.

Exercise Purpose: This is the word-level version of character counting. It introduces Frequency Mapping at scale, which underpins search engine indexing and “word cloud” generation.

Given Input: str1 = "apple banana apple cherry banana apple"

Expected Output: {'apple': 3, 'banana': 2, 'cherry': 1}

str1 = "apple banana apple cherry banana apple"
words = str1.lower().split()
word_count = {}

for word in words:
    # Get the current count (default to 0 if not found) and add 1
    word_count[word] = word_count.get(word, 0) + 1

print(word_count)Code language: Python (python)

Exercise 37. First Non-Repeating Character

Practice Problem: Find the first character in a string that does not repeat anywhere else.

Exercise Purpose: This exercise demonstrates Multi-Pass Algorithms. You cannot solve this in a single pass because you won’t know if a character repeats until you see the whole string. It teaches you to use a frequency map to guide a second traversal.

Given Input: str1 = "swiss"

Expected Output: w

def first_unique(s):
    counts = {}
    # First pass: count frequencies
    for char in s:
        counts[char] = counts.get(char, 0) + 1
    
    # Second pass: check order
    for char in s:
        if counts[char] == 1:
            return char
    return None

print("First unique in 'swiss':", first_unique("swiss"))Code language: Python (python)

Exercise 38. String Rotation Check

Practice Problem: Write a program to check if one string is a rotation of another (e.g., “waterbottle” is a rotation of “erbottlewat”).

Exercise Purpose: This exercise teaches Algorithmic Cleverness. While you could try to rotate the string manually in a loop, there is a “cheat code” logic that involves string concatenation, which is much more efficient.

Given Input: s1 = "waterbottle" s2 = "erbottlewat"

Expected Output: Is Rotation: True

def is_rotation(s1, s2):
    # Rotations must be the same length
    if len(s1) != len(s2):
        return False
    
    # Double the first string
    combined = s1 + s1
    
    # Check if s2 is inside the doubled version
    return s2 in combined

s1 = "waterbottle"
s2 = "erbottlewat"
print(f"Is '{s2}' a rotation of '{s1}'? {is_rotation(s1, s2)}")Code language: Python (python)