Algorithms
The true test of problem solving: when one realizes that time and memory aren’t infinite.
Warmup
| Name | Preview | Code | Difficulty |
|---|---|---|---|
| Solve Me First | This is an easy challenge to help you start coding in your favorite languages! | C++ Haskell Java Javascript Python bash | Easy |
| Simple Array Sum | Calculate the sum of integers in an array. | C++ Python | Easy |
| Compare the Triplets | Compare the elements in two triplets. | C++ Python | Easy |
| A Very Big Sum | Calculate the sum of the values in an array that might exceed the range of int values. | Python | Easy |
| Diagonal Difference | Calculate the absolute difference of sums across the two diagonals of a square matrix. | Python | Easy |
| Plus Minus | Calculate the fraction of positive, negative and zero values in an array. | Python | Easy |
| Staircase | Print a right-aligned staircase with n steps. | Python | Easy |
| Mini-Max Sum | Find the maximum and minimum values obtained by summing four of five integers. | Python | Easy |
| Birthday Cake Candles | Determine the number of candles that are blown out. | Python | Easy |
| Time Conversion | Convert time from an AM/PM format to a 24 hour format. | Python | Easy |
Implementation
| Name | Preview | Code | Difficulty |
|---|---|---|---|
| Grading Students | Round student grades according to Sam’s rules. | Python | Easy |
| Apple and Orange | Find the respective numbers of apples and oranges that fall on Sam’s house. | Python | Easy |
| Kangaroo | Can two kangaroo meet after making the same number of jumps? | Python | Easy |
| Between Two Sets | Find the number of integers that satisfies certain criteria relative to two sets. | Python | Easy |
| Breaking the Records | Given an array of Maria’s basketball scores all season, determine the number of times she breaks her best and worst records. | Python | Easy |
| Birthday Chocolate | Given an array of integers, find the number of subarrays of length k having sum s. | Python | Easy |
| Divisible Sum Pairs | Count the number of pairs in an array having sums that are evenly divisible by a given number. | Python | Easy |
| Migratory Birds | Determine which type of bird in a flock occurs at the highest frequency. | Python | Easy |
| Day of the Programmer | Given year, determine date of the 256th day of the year. | Python | Easy |
| Bon Appétit | Determine whether or not Brian overcharged Anna for their split bill. | Python | Easy |
| Sock Merchant | How many pairs of socks John can sell? | Python | Easy |
| Drawing Book | How many pages does Brie need to turn to get to page p? | Python | Easy |
| Counting Valleys | Count the valleys encountered during vacation. | C++ | Easy |
| Electronics Shop | Determine the most expensive Keyboard and USB drive combination Monica can purchase within her budget. | C++ | Easy |
| Cats and a Mouse | Which cat will catch the mouse first? | Python | Easy |
| Forming a Magic Square | Find the minimum cost of converting a 3 by 3 matrix into a magic square. | Python | Medium |
| Picking Numbers | What’s the largest size subset can you choose from an array such that the difference between any two integers is not bigger than 1? | Python | Easy |
| Climbing the Leaderboard | Help Alice track her progress toward the top of the leaderboard! | Python | Medium |
| The Hurdle Race | Can you help Dan determine the minimum number of magic beverages he must drink to jump all the hurdles? | Python | Easy |
| Designer PDF Viewer | Help finding selection area in PDF Viewer. | Python | Easy |
| Utopian Tree | Predict the height of the tree after N growth cycles. | Python | Easy |
| Angry Professor | Decide whether or not the class will be canceled based on the arrival times of its students. | Python | Easy |
| Beautiful Days at the Movies | Find the number of beautiful days. | Python | Easy |
| Viral Advertising | How many people will know about the new product after n days? | Python | Easy |
| Save the Prisoner! | Given M sweets and a circular queue of N prisoners, find the ID of the last prisoner to receive a sweet. | Python | Easy |
| Circular Array Rotation | Print the elements in an array after ‘m’ right circular rotation operations. | Python | Easy |
| Sequence Equation | Find some y satisfying p(p(y)) = x for each x from 1 to n. | Python | Easy |
| Jumping on the Clouds: Revisited | Determine the amount of energy Aerith has after the cloud game ends. | Python | Easy |
| Find Digits | Calculate the number of digits in an integer that evenly divide it. | Python | Easy |
| Extra Long Factorials | Calculate a very large factorial that doesn’t fit in the conventional numeric data types. | Haskell Python | Medium |
| Append and Delete | Can you convert $s$ to $t$ by performing exactly $k$ operations? | Python | Easy |
| Sherlock and Squares | Find the count of square numbers between A and B | Python | Easy |
| Library Fine | Help your library calculate fees for late books! | Python | Easy |
| Cut the sticks | Given the lengths of n sticks, print the number of sticks that are left before each cut operation. | Python | Easy |
| Non-Divisible Subset | Find the size of the maximal non-divisible subset. | Python | Medium |
| Repeated String | Find and print the number of letter a’s in the first n letters of an infinitely large periodic string. | Python | Easy |
| Jumping on the Clouds | Jumping on the clouds | Python | Easy |
| Equalize the Array | Delete a minimal number of elements from an array so that all elements of the modified array are equal to one another. | Python | Easy |
| Queen’s Attack II | Find the number of squares the queen can attack. | Python | Medium |
| ACM ICPC Team | Print the maximum topics a given team can cover for ACM ICPC World Finals | Python | Easy |
| Taum and B’day | Calculate the minimum cost required to buy some amounts of two types of gifts when costs of each type and the rate of conversion from one form to another is provided. | Python | Easy |
| Organizing Containers of Balls | Determine if David can perform some sequence of swap operations such that each container holds one distinct type of ball. | Python | Medium |
| Encryption | Encrypt a string by arranging the characters of a string into a matrix and printing the resulting matrix column wise. | Python | Medium |
| Bigger is Greater | Rearrange the letters of a string to construct another string such that the new string is lexicographically greater than the original. | Python | Medium |
| Modified Kaprekar Numbers | Print kaprekar numbers in the given range | Python | Easy |
| Beautiful Triplets | Python | Easy | |
| Minimum Distances | Find the minimum distance between two different indices containing the same integers. | Python | Easy |
| Halloween Sale | How many games can you buy during the Halloween Sale? | Python | Easy |
| The Time in Words | Display the time in words. | Python | Medium |
| Chocolate Feast | Calculate the number of chocolates that can be bought following the given conditions. | Python | Easy |
| Service Lane | Calculate the maximum width of the vehicle that can pass through a service lane. | Python | Easy |
| Lisa’s Workbook | A workbook with chapters. Some number of problems per page. How many problems have a number equal to a page’s number? | Python | Easy |
| Flatland Space Stations | Find the maximum distance an astronaut needs to travel to reach the nearest space station. | Python | Easy |
| Fair Rations | How many loaves of bread will it take to feed your subjects? | Python | Easy |
| Cavity Map | Depict cavities on a square map | C++ | Easy |
| Manasa and Stones | Calculate the possible values of the last stone where consecutive values on the stones differ by a value ‘a’ or a value ‘b’. | Python | Easy |
| The Grid Search | Given a 2D array of digits, try to find a given 2D grid pattern of digits within it. | Python | Medium |
| Happy Ladybugs | Determine whether or not all the ladybugs can be made happy. | Python | Easy |
| Strange Counter | Print the value displayed by the counter at a given time, $t$. | Python | Easy |
| Absolute Permutation | Find lexicographically smallest absolute permutation. | Python | Medium |
| Ema’s Supercomputer | Determine the product of the areas of two pluses on a grid. | C++ | Medium |
| Larry’s Array | Larry | Python | Medium |
| Almost Sorted | Sort an array by either swapping or reversing a segment | Python | Medium |
| Matrix Layer Rotation | Rotate the matrix R times and print the resultant matrix. | Python | Hard |
Strings
| Name | Preview | Code | Difficulty |
|---|---|---|---|
| Super Reduced String | Given a string, repeatedly remove adjacent pairs of matching characters and then print the reduced result. | Python | Easy |
| CamelCase | Python | Easy | |
| Strong Password | How many characters should you add to make the password strong? | Python | Easy |
| Two Characters | Print the length of the longest possible string $t$ you can form. | Python | Easy |
| Caesar Cipher | Encrypt a string by rotating the alphabets by a fixed value in the string. | Python | Easy |
| Mars Exploration | Save Our Ship! | Python | Easy |
| HackerRank in a String! | Determine if a string contains a subsequence of characters that spell “hackerrank”. | Python | Easy |
| Pangrams | Check whether a given string is a panagram or not. | Python | Easy |
| Weighted Uniform Strings | Determine if a string contains uniform substrings of certain weights. | Python | Easy |
| Separate the Numbers | Determine if a numeric string can be broken into a sequence of increasing numbers. | Python | Easy |
| Funny String | Is the absolute difference between consecutive characters is the same for a string and the reverse of that string for all indices. | Python | Easy |
| Gemstones | Find the number of different gem-elements present. | Python | Easy |
| Alternating Characters | Calculate the minimum number of deletions required to convert a string into a string in which consecutive characters are different. | Python | Easy |
| Beautiful Binary String | How many binary characters must you change to remove every occurrence of “010” from a binary string? | Python | Easy |
| The Love-Letter Mystery | Find the minimum number of operations required to convert a given string into a palindrome under certain conditions | Python | Easy |
| Determining DNA Health | Determine which weighted substrings in a subset of substrings can be found in a given string and calculate the string’s total weight. | Python | Hard |
| Palindrome Index | Determine which character(s) must be removed to make a string a palindrome. | Python | Easy |
| Anagram | Find the minimum number of characters of the first string that we need to change in order to make it an anagram of the second string. | Python | Easy |
| Making Anagrams | How many characters should one delete to make two given strings anagrams of each other? | Python | Easy |
| Game of Thrones - I | Check whether any anagram of a string can be a palindrome or not. | Python | Easy |
| Two Strings | Given two strings, you find a common substring of non-zero length. | Python | Easy |
| String Construction | Find the minimum cost of copying string s. | Python | Easy |
| Sherlock and the Valid String | Remove some characters from the string such that the new string’s characters have the same frequency. | Python | Medium |
| Highest Value Palindrome | Make a number palindromic in no more than $k$ moves, maximal. | Python | Medium |
| Sherlock and Anagrams | Find the number of unordered anagramic pairs of substrings of a string. | Python | Medium |
| Common Child | Given two strings a and b of equal length, what’s the longest string (s) that can be constructed such that s is a child to both a and b? | C++ Python | Medium |
| Morgan and a String | Find the lexicographically minimal string that can be formed by the combination of two strings. | C | Expert |
Sorting
| Name | Preview | Code | Difficulty |
|---|---|---|---|
| Big Sorting | Sort an array of very long numeric strings. | Python | Easy |
| Intro to Tutorial Challenges | Introduction to the Tutorial Challenges | Python | Easy |
| Insertion Sort - Part 1 | Insert an element into a sorted array. | Python | Easy |
| Insertion Sort - Part 2 | Code Insertion Sort itself. | Python | Easy |
| Correctness and the Loop Invariant | How do you demonstrate the correctness of an algorithm? You can use the loop invariant. | Python | Easy |
| Running Time of Algorithms | The running time of Algorithms in general and Insertion Sort in particular. | Python | Easy |
| Quicksort 1 - Partition | Perform the first step of Quicksort: partitioning an array. | Python | Easy |
| Counting Sort 1 | Count the number of times each value appears. | Python | Easy |
| Counting Sort 2 | Simple version of counting sort. | Python | Easy |
| The Full Counting Sort | The real counting sort. | Python | Medium |
| Closest Numbers | Find the closest numbers in a list. | Python | Easy |
| Find the Median | Find the Median in a list of numbers. | Python | Easy |
| Insertion Sort Advanced Analysis | How many shifts will it take Insertion Sort to sort an array? | C++ Python | Advanced |
Search
| Name | Preview | Code | Difficulty |
|---|---|---|---|
| Hackerland Radio Transmitters | Find the minimum number of radio transmitters needed to cover all the houses in Hackerland! | Python | Medium |
| Ice Cream Parlor | Help Sunny and Johnny spend all their money during each trip to the Ice Cream Parlor. | Python | Easy |
| Missing Numbers | Find the numbers missing from a sequence given a permutation of the original sequence | Python | Easy |
| Pairs | Given N numbers, count the total pairs of numbers that have a difference of K. | Python | Medium |
| Sherlock and Array | Check whether there exists an element in the array such that sum of elements on its left is equal to the sum of elements on its right. | Python | Easy |
Greedy
| Name | Preview | Code | Difficulty |
|---|---|---|---|
| Minimum Absolute Difference in an Array | Given a list of integers, calculate their differences and find the difference with the smallest absolute value. | Python | Easy |
| Marc’s Cakewalk | Find the minimum number of miles Marc must walk to burn the calories consumed from eating cupcakes. | Python | Easy |
| Grid Challenge | Find if it is possible to rearrange a square grid such that every row and every column is lexicographically sorted. | Python | Easy |
| Maximum Perimeter Triangle | Find the triangle having the maximum perimeter. | C++ | Easy |
| Beautiful Pairs | Change an element of B and calculate the number of pairwise disjoint beautiful pairs. | Python | Easy |
| Sherlock and The Beast | Find the largest number following some rules having N digits. | Python | Easy |
Dynamic Programming
| Name | Preview | Code | Difficulty |
|---|---|---|---|
| Fibonacci Modified | Compute the nth term of a Fibonacci sequence. | Python | Medium |
| The Longest Increasing Subsequence | Find the length of the longest increase subsequence in a given array. | C++ | Advanced |
| Dorsey Thief | standard knapsack problem | C++ | Advanced |
Constructive Algorithms
| Name | Preview | Code | Difficulty |
|---|---|---|---|
| New Year Chaos | Determine how many bribes took place to get a queue into its current state. | Python | Medium |
Bit Manipulation
| Name | Preview | Code | Difficulty |
|---|---|---|---|
| Lonely Integer | Find the unique element in an array of integer pairs. | Python | Easy |
| Maximizing XOR | Given two integers, L and R, find the maximal value of A xor B, where A and B satisfy a condition. | Python | Easy |
| Counter game | Louise and Richard play a game, find the winner of the game. | Python | Medium |
| The Great XOR | Count the number of non-negative integer a’s that are less than some x where the bitwise XOR of a and x is greater than x. | C++ | Medium |
| Flipping bits | Flip bits in its binary representation. | C++ | Easy |
| A or B | A or B = C | Python | Medium |
| Hamming Distance | You are given a string S, consisting of N small latin letters ‘a’ and ‘b’. Process the given M queries. | C++ | Expert |
Game Theory
| Name | Preview | Code | Difficulty |
|---|---|---|---|
| Game of Stones | A Game of Stones | Python | Easy |
Debugging
| Name | Preview | Code | Difficulty |
|---|---|---|---|
| Prime Dates | Find the number of prime dates in a range | C++ Java Python | Medium |
| Zig Zag Sequence | Find a zig zag sequence of the given array. | C++ Java Python | Medium |