Programming Exercises¶
This document features simple programming exercises to sharpen your skills in foundational concepts like strings, numbers, lists, and algorithms. Ideal for:
- Learning a new programming language by implementing hands-on solutions.
- Refreshing skills in a language you haven’t used recently.
- Preparing for coding interviews as a stepping stone to platforms like LeetCode or HackerRank.
- Building confidence with approachable problems before tackling advanced ones.
- Improving problem-solving, debugging, and optimization skills.
- Practicing unit testing, a crucial skill for software engineering.
Problem 1: Vowel Counter¶
Write a program that counts the number of vowels in a given word. Vowels are a, e, i, o, u (case-insensitive).
Examples:
Input: "hello"
Output: 2
Input: "EducaTiOn"
Output: 5
Input: "rhytHm"
Output: 0
Input: "aQuAriUm"
Output: 5
Input: "PYTHON"
Output: 1
Input: "cOmpUtEr"
Output: 3
Input: "12345abc"
Output: 1
Input: ""
Output: 0
Input: "aeiouAEIOU"
Output: 10
Input: "sTrAwbErrY"
Output: 2
Problem 2: Reverse a List¶
Write a function to reverse a list of numbers.
Examples:
Input: [1, 2, 3, 4, 5]
Output: [5, 4, 3, 2, 1]
Input: [10, 20, 30]
Output: [30, 20, 10]
Input: []
Output: []
Input: [7]
Output: [7]
Input: [1, 1, 1, 1]
Output: [1, 1, 1, 1]
Input: [-1, -2, -3, -4]
Output: [-4, -3, -2, -1]
Input: [0, 100, 200]
Output: [200, 100, 0]
Input: [3, 5, 2, 9]
Output: [9, 2, 5, 3]
Input: [42]
Output: [42]
Input: [8, 6, 7, 5, 3, 0, 9]
Output: [9, 0, 3, 5, 7, 6, 8]
Problem 3: String Reversal¶
Write a function to reverse a string.
Examples:
Input: "hello"
Output: "olleh"
Input: ""
Output: ""
Input: "madam"
Output: "madam"
Input: "hello world!"
Output: "!dlrow olleh"
Input: " abc "
Output: " cba "
Input: "Python"
Output: "nohtyP"
Problem 4: Perfect Square¶
Check if a number is a perfect square. A perfect square is a non-negative integer that is the square of another integer.
Examples:
Input: 25
Output: True
Explanation: 25 (5 * 5 = 25)
Input: 18
Output: False
Input: 0
Output: True (0 * 0 = 0)
Input: 4
Output: True
Input: 15
Output: False
Input: 16
Output: True
Input: 101
Output: False
Input: 10000
Output: True
Input: -1
Output: False (A perfect square must be non-negative)
Problem 5: Second Largest¶
Find the second largest number in an array.
Assume that the input array contains at least two numbers.
Examples:
Input: [10, 5, 8, 12]
Output: 10
Input: [1, 2, 3, 4, 5]
Output: 4
Input: [5, 5, 5, 5]
Output: 5
Input: [5, 3, 0, 5]
Output: 5
Input: [1, 2]
Output: 1
Input: [-1, -2, -3]
Output: -2
Input: [5, 10, 15, 20, 25]
Output: 20
Input: [3, 1, 4, 2]
Output: 3
Input: [0, -1, -2, -3]
Output: -1
Input: [42, 35, 35, 42, 35, 35]
Output: 42
Problem 6: Digital Root¶
Add all digits in a number until you get a single digit.
Examples:
Input: 789
Output: 6 (7+8+9=24, 2+4=6)
Input: 1234
Output: 1 (1+2+3+4=10, 1+0=1)
Input: 5
Output: 5
Input: 100
Output: 1
Explanation: 1 + 0 + 0 = 1.
Input: 456
Output: 6
Explanation: 4 + 5 + 6 = 15, 1 + 5 = 6.
Input: 1001
Output: 2
Explanation: 1 + 0 + 0 + 1 = 2.
Input: 98765
Output: 8
Explanation: 9 + 8 + 7 + 6 + 5 = 35, 3 + 5 = 8.
Input: 123456789
Output: 9
Explanation: 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = 45, 4 + 5 = 9.
Input: 999999999
Output: 9
Explanation: 9 repeated 9 times adds up to 81, 8 + 1 = 9.
Problem 7: Extra Character¶
Given two strings, A and B, where A is a string that contains all the characters of B in the same order, plus exactly one additional character at a random position, find the extra character in A.
Examples:
Input: A = "atcb42c", B = "atb42c"
Output: "c"
Input: A = "abcd", B = "abc"
Output: "d"
Input: A = "aabbcc", B = "aabcc"
Output: "b"
Input: A = "xylophone", B = "xylophne"
Output: "o"
Input: A = "12345", B = "1234"
Output: "5"
Input: A = "a", B = ""
Output: "a"
Input: A = "HellO", B = "HelO"
Output: "l"
Problem 8: Number Triangle¶
Print a triangle pattern of numbers where each row contains increasing numbers starting from 1.
Examples:
Input: 1
Output:
1
Input: 3
Output:
1
1 2
1 2 3
Input: 5
Output:
1
1 2
1 2 3
1 2 3 4
1 2 3 4 5
Input: 7
Output:
1
1 2
1 2 3
1 2 3 4
1 2 3 4 5
1 2 3 4 5 6
1 2 3 4 5 6 7
Problem 9: Longest Common Prefix¶
Write a function to find the longest prefix shared by all strings in an array. A prefix is the beginning part of a string. For example, the prefixes of "car" are "c", "ca", and "car".
If no common prefix exists, return an empty string "".
Examples::
Input: ["beaux", "beauty", "beat", "beam"]
Output: "bea"
Input: ["apple", "ape", "april"]
Output: "ap"
Input: ["test", "testing", "tester"]
Output: "test"
Input: ["hello", "world", "python"]
Output: ""
Input: ["short", "longer", "different"]
Output: ""
Input: ["prefix", "preference", ""]
Output: ""
Input: ["test", "test", "test"]
Output: "test"
Input: []
Output: ""
Input: ["fun"]
Output: "fun"
Problem 10: Split Array with Two Sets¶
Given an integer array, the task is to determine whether it can be split into two parts such that each part contains only distinct elements.
Examples:
Input: [10, 10, 20, 20, 30, 40]
Output: True
Explanation: One possible split into [10, 20, 30] and [10, 20, 40].
Both parts have distinct elements.
Input: [1, 1, 1, 1]
Output: False
Input: [1, 2, 3, 4, 5, 6]
Output: True
Explanation: One possible split is [1, 2, 3] and [4, 5, 6].
Input: [1, 1, 1, 2, 2, 2]
Output: False
Explanation: No way to split into two parts with distinct elements in each.
Input: [1]
Output: True
Explanation: The array can be split into [1] and an empty set.
Input: []
Output: True
Explanation: An empty array trivially satisfies the condition.
Input: [6, 6]
Output: True
Explanation: The array can be split as [6] and [6].
Input: [3, 4, 3, 4]
Output: True
Explanation: The array can be split as [3, 4] and [3, 4].
Problem 11: Reverse Words¶
Given a sentence, reverse the order of words. Trim leading and trailing spaces, and reduce multiple spaces to a single space between words.
Examples:
Input: "The quick brown fox"
Output: "fox brown quick The"
Input: "Hello world!"
Output: "world! Hello"
Input: " Python is fun "
Output: "fun is Python"
Input: "Single"
Output: "Single"
Problem 12: Find the Missing Number¶
Given an array containing n distinct numbers taken from the range [0, n], find the missing number.
Examples:
Problem 13: Rearrange Vowels¶
Write a function to rearrange the vowels in a string in alphabetical order, placing uppercase vowels before lowercase vowels. Keep all consonants in their original positions.
Examples:
Input: s = "coding"
Output: "cidong"
Input: s = "AaEeIiOoUu"
Output: "AEIOUaeiou"
Input: s = "alphabet"
Output: "alphabet"
Input: s = "alphabEt"
Output: "Elphabat"
Problem 14: First Unique Character¶
Given a string, find the index of the first unique character. Return -1 if no such character exists.
Examples:
Problem 15: Reverse Digits of a Number¶
Write a function to reverse the digits of an integer.
Examples:
Problem 16: Minimum Common Value¶
You are given two sorted integer arrays, nums1 and nums2. Both are in non-decreasing order. Find the smallest integer that appears in both arrays. If there is no common element, return -1.
Examples:
Input: nums1 = [1, 2, 3], nums2 = [2, 4]
Output: 2
Input: nums1 = [1, 2, 3, 6], nums2 = [2, 3, 4, 4]
Output: 2
Input: nums1 = [1, 3, 5], nums2 = [2, 4, 6]
Output: -1
Problem 17: Add Two Numbers Represented as Strings¶
Write a function to add two numbers represented as strings. Return the sum as a string.
Examples:
Problem 18: Sum of Array Except Self¶
Given an array of integers, return a new array such that each element at index i is the sum of all numbers in the original array except the one at i.
Examples:
Problem 19: Check for Palindrome¶
Write a function to check if a given string is a palindrome.
Examples:
Problem 20: Check if Two Strings are Anagrams¶
Write a function to check if two strings are anagrams of each other.
Examples:
Problem 21: Phone Number Formatter¶
Write a program that formats a 10-digit phone number into the format (XXX) XXX-XXXX.
Examples:
Problem 22: FizzBuzz String¶
Write a function fizzbuzz_string(n) that returns a single string containing the FizzBuzz sequence from 1 to n, separated by commas.
- For multiples of 3, use "Fizz".
- For multiples of 5, use "Buzz".
- For multiples of both 3 and 5, use "FizzBuzz".
- Otherwise, just use the number itself.
Example:
Problem 23: Diamond Pattern¶
Print a diamond pattern using asterisks (*).
Examples:
Input: 3
Output:
*
***
*****
***
*
Input: 5
Output:
*
***
*****
*******
*********
*******
*****
***
*
Problem 24: Check if a String is a Pangram¶
A pangram is a sentence that contains every letter of the English alphabet at least once.
Write a function to determine whether a given string is a pangram. The check should be case-insensitive.
Examples:
Input: "The quick brown fox jumps over the lazy dog"
Output: True
Input: "Pack my box with five dozen liquor jugs 1234!!!"
Output: True
Explanation: Numbers and punctuation are ignored, and all letters are present at least once.
Input: "The quick brown fox jumps over the la dog"
Output: False
Problem 25: Date String Formatter¶
Write a function reformat_date(date_str) that takes a string in the format YYYY-MM-DD and returns a string in the format MonthName DD, YYYY, where MonthName is the full English month (e.g., "January", "February", …).
Examples:
Problem 26: Compute Double Factorial¶
Write a function that computes the double factorial of a given non-negative integer n.
The double factorial of n, denoted as n!!, is defined as the product of all integers from 1 to n that have the same parity (odd or even) as n.
Examples:
Input: n = 8
Output: 384
Explanation: 8!! = 8 * 6 * 4 * 2 = 384
Input: n = 7
Output: 105
Explanation: 7!! = 7 * 5 * 3 * 1 = 105
Problem 27: Check Derangement¶
Write a function to check if one permutation of a string is a derangement of another. A derangement means no character appears in its original position.
Examples:
Problem 28: Check Narcissistic Number¶
Write a function to check if a number is a narcissistic number. A number is narcissistic if the sum of its digits raised to the power of the number of digits equals the number itself.
Example:
Problem 29: Count Unique Characters in a String¶
Write a function that counts the number of unique characters in a string.
Examples:
Problem 30: Password Validator¶
Write a function that validates if a password meets all the following rules:
- Minimum length of 8 characters
- Contains at least one uppercase letter
- Contains at least one lowercase letter
- Contains at least one digit
- Contains at least one special character from @#$%^&*!
- No white-space allowed
Examples:
Input: "Pass123!"
Output: True
Input: "weakpass"
Output: False
Input: "NoSpecial123"
Output: False
Input: "Short1!"
Output: False
Input: "Pass 123!"
Output: False (contains space)
Problem 31: Most Frequent Digit¶
Given a positive integer, determine which digit occurs most frequently. If there is a tie, return the smallest digit.
Examples:
Input: 112233
Output: 1
Explanation: Digits 1, 2, and 3 occur twice, so the smallest digit (1) is returned.
Input: 9876543211
Output: 1
Problem 32: Geometric Sequence¶
Write a function to generate the first n terms of a geometric progression, given the first term a and common ratio r.
Examples:
Input: a = 3, r = 2, n = 5
Output: [3, 6, 12, 24, 48]
Input: a = 1, r = 0.5, n = 4
Output: [1, 0.5, 0.25, 0.125]
Problem 33: Word Chain¶
A list of words is valid if each word starts with the last letter of the previous word. Write a function to check if the given sequence of words is valid.
Assume the words are case-insensitive.
Examples:
Input: ["hello", "orange", "elephant", "tree"]
Output: True
Explanation: "hello" -> "orange" -> "elephant" -> "tree".
Input: ["cat", "dog", "pig", "goat"]
Output: False
Explanation: "dog" does not start with "t".
Input: ["Apple", "Elephant", "tiger"]
Output: True
Explanation: Case is ignored, so "Apple" -> "Elephant" -> "tiger" is valid.
Input: ["zebra"]
Output: True
Explanation: A single word is trivially valid.
Input: []
Output: True
Explanation: An empty list is trivially valid.
Problem 34: Detect Cyclic Words¶
Write a function to check if two strings are cyclic permutations of each other. Two strings are cyclic permutations if one string can be rotated to match the other.
Examples:
Input: s1 = "abcde", s2 = "deabc"
Output: True
Explanation: Rotating "deabc" gives "abcde".
Input: s1 = "hello", s2 = "lohel"
Output: True
Input: s1 = "hello", s2 = "lolhe"
Output: False
Problem 35: Alternating Sum of Digits¶
Write a function to calculate the alternating sum of digits in an integer. Alternate between adding and subtracting each digit from left to right.
Examples:
Problem 36: Longest Increasing Subarray¶
A subarray is a contiguous portion of an array. For example, in the array [1, 2, 3, 4], [1, 2] and [3, 4] are subarrays, but [1, 3] is not because the elements are not contiguous.
Write a function to find the length of the longest subarray in a list of integers where the elements are strictly increasing.
Examples:
Input: [1, 2, 3, 1, 2]
Output: 3
Explanation: The subarray [1, 2, 3] is the longest increasing subarray.
Input: [5, 1, 2, 3, 0]
Output: 3
Explanation: The subarray [1, 2, 3] is the longest.
Problem 37: Peak Indices¶
You are given a 0-indexed integer array, nums. You need to find all indices i (except the first and last) such that nums[i] > nums[i - 1] and nums[i] > nums[i + 1].
Examples:
Input: [1, 4, 3, 8, 5]
Output: [1, 3]
Explanation: nums[0] and nums[4] cannot be peaks because they are
the first and last elements. nums[1] and nums[3] are strictly greater
than their neighboring elements.
Input: [2, 4, 4]
Output: []
Explanation: nums[0] and nums[2] cannot be peaks because they are
the first and last elements. nums[1] also can not be a peak because
it is not strictly greater than nums[2].
Input: [5, 2, 3, 1, 4]
Output: [2]
Input: [1, 2, 3, 2, 1]
Output: [2]
Problem 38: Cyclic Shifting¶
You are given a string s and an integer k. Your task is to shift the characters of the string s cyclically to the right by k positions. If the end of the string is reached during the shift, wrap around to the beginning.
Write a function that takes s and k as input and returns the resulting string after the cyclic shift.
Examples:
Input: s = "hello", k = 2
Output: "llohe"
Explanation:
For i = 0, the 2nd character after 'h' is 'l'.
For i = 1, the 2nd character after 'e' is 'l'.
For i = 2, the 2nd character after 'l' is 'o'.
For i = 3, the 2nd character after 'l' is 'h'.
For i = 4, the 2nd character after 'o' is 'e'.
Input: s = "abcdef", k = 4
Output: "efabcd"
Explanation:
For i = 0, the 4th character after 'a' is 'e'.
For i = 1, the 4th character after 'b' is 'f'.
For i = 2, the 4th character after 'c' is 'a'.
For i = 3, the 4th character after 'd' is 'b'.
For i = 4, the 4th character after 'e' is 'c'.
For i = 5, the 4th character after 'f' is 'd'.
Input: s = "xxxx", k = 1
Output: "xxxx"
Problem 39: Matrix Diagonal Sum¶
You are given a square matrix mat of size \(n \times n\). Your task is to return the sum of the matrix diagonals.
- Include the primary diagonal (top-left to bottom-right) and the secondary diagonal (top-right to bottom-left). - If the same element is on both diagonals (e.g., the center of an odd-sized matrix), only count it once.
Examples:
Input: [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
Output: 25
Explanation:
- Primary diagonal: 1 + 5 + 9 = 15
- Secondary diagonal: 3 + 5 + 7 = 15
- Since the center element (5) is counted twice, subtract it once: 15 + 15 - 5 = 25.
Input: [
[1, 1, 1, 1],
[1, 1, 1, 1],
[1, 1, 1, 1],
[1, 1, 1, 1]
]
Output: 8
Explanation:
- Primary diagonal: 1 + 1 + 1 + 1 = 4
- Secondary diagonal: 1 + 1 + 1 + 1 = 4
- No overlap since the matrix has an even size.
Total: 4 + 4 = 8
Input: [[5]]
Output: 5
Problem 40: Smallest Even Multiple¶
Given a positive integer n, return the smallest positive integer that is a multiple of both 2 and n.
Examples:
Input: 5
Output: 10
Explanation: The smallest multiple of both 5 and 2 is 10.
Input: 12
Output: 12
Explanation: The smallest multiple of both 12 and 2 is 12.
Problem 41: Arithmetic Progression¶
Given an array of integers, determine if the numbers form an arithmetic progression (a sequence where the difference between consecutive terms is constant).
Examples:
Input: [3, 7, 11, 15]
Output: True
Explanation: The difference between consecutive terms is 4.
Input: [1, 2, 4]
Output: False
Problem 42: Run-Length Encoding¶
Write a function to compress a string using run-length encoding.
Example:
Problem 43: Majority Element¶
Given an array of length n, find the majority element. The majority element is the element that appears more than ⌊n/2⌋ times.
Assume the array always has a majority element.
Examples:
Problem 44: Longest Monotonic Subarray¶
You are given a 0-indexed integer array, nums. A subarray is a contiguous portion of the array. We say a subarray is:
- Strictly Increasing if each element is greater than the one before it.
- Strictly Decreasing if each element is less than the one before it.
Your task is to find the length of the longest subarray that is strictly increasing or strictly decreasing.
Examples:
Input: [2, 2, 2]
Output: 1
Explanation: No two consecutive elements are strictly increasing or strictly decreasing,
so the longest valid subarray is just any single element.
Input: [1, 2, 3, 4]
Output: 4
Explanation: The entire array [1, 2, 3, 4] is strictly increasing.
Input: [5, 6, 5, 4, 3, 10]
Output: 4
Explanation: [6, 5, 4, 3] is strictly decreasing (length 4).
Input: [1, 3, 5, 4, 2]
Output: 3
Problem 45: Perfect Square¶
Given an n x n grid where each cell contains an integer from 1 to n, determine whether every row and every column contains all integers from 1 to n.
Examples:
Input: [[1, 2, 3], [3, 1, 2], [2, 3, 1]]
Output: True
Explanation: In this case, n = 3, and every row and column contains the
numbers 1, 2, and 3.
Input: [[1, 2, 2], [3, 1, 2], [2, 3, 1]]
Output: False
Explanation: In this case, n = 3, but the first row has a repeated 2.
Problem 46: Largest Sum of Non-Adjacent Numbers¶
Given a list of integers, write a function that returns the largest sum of two non-adjacent numbers.
Examples:
Problem 47: Array Rotation¶
Rotate an array by k positions to the right.
Examples:
Input: [1, 2, 3, 4], k = 2
Output: [3, 4, 1, 2]
Input: [10, 20, 30, 40, 50], k = 3
Output: [30, 40, 50, 10, 20]
Input: [1, 2, 3], k = 0
Output: [1, 2, 3]
Input: [1, 2, 3], k = 3
Output: [1, 2, 3]
Input: [10, 20, 30, 40, 50], k = 1
Output: [50, 10, 20, 30, 40]
Input: [], k = 3
Output: []
Input: [7, 8, 9], k = 10
Output: [9, 7, 8]
Problem 48: Largest Alphabetical Rotation¶
Given a string s, generate all rotations (cyclic shifts) of s and return the lexicographically largest rotation.
Examples:
Problem 49: Sort by Age¶
Given two arrays - one containing names and another containing corresponding ages - write a function to sort people by their ages in descending order. Return the sorted list of names.
Assume the values of ages are distinct.
Examples:
Input: names = ["Alice", "Bob", "Charlie"], ages = [24, 45, 70]
Output: ["Charlie", "Bob", "Alice"]
Input: names = ["Mark", "Emma", "Alex", "Sarah"], ages = [75, 18, 41, 65]
Output: ["Mark", "Sarah", "Alex", "Emma"]
Problem 50: Partition String into Fixed-Size Groups¶
Given a string s, an integer k, and a fill character fill, partition s into groups of size k. If the length of s is not a multiple of k, pad the final group with the fill character until it has size k. Return all the groups as a list of strings.
Examples:
Input: s = "hello", k = 2, fill = "*"
Output: ["he", "ll", "o*"]
Explanation: The remainder has only 'o', so we add one '*' to form a group of size 2.
Input: s = "abcd123", k = 3, fill = "-"
Output: ["abc", "d12", "3--"]
Explanation: String length is 7, so we need 2 fill characters '-' to complete the last group.