Every problem
90 problems in three tracks, each ordered from easiest to hardest. Every one has a hint and a full solution. The daily problem works through them one day at a time.
Python
- Python 1 Reverse the words Easy
- Python 2 FizzBuzz, as a list Easy
- Python 3 Sum of the digits Easy
- Python 4 Running total Easy
- Python 5 Capitalise each word Easy
- Python 6 Real palindromes Easy
- Python 7 Is it an anagram? Easy
- Python 8 Most common character Easy
- Python 9 Count the words Easy
- Python 10 Remove duplicates, keep order Easy
- Python 11 Transpose a matrix Easy
- Python 12 Fast Fibonacci Easy
- Python 13 Rotate a list Easy
- Python 14 Chunk a list Medium
- Python 15 Flatten a nested list Medium
- Python 16 The default argument trap Medium
- Python 17 The copied grid Medium
- Python 18 Run-length encoding Medium
- Python 19 Caesar cipher Medium
- Python 20 Invert a dictionary Medium
- Python 21 Removing while looping Medium
- Python 22 Late-binding lambdas Medium
- Python 23 Sieve of Eratosthenes Medium
- Python 24 Roman numerals Medium
- Python 25 Write a memoize decorator Hard
- Python 26 Flatten a dictionary Hard
- Python 27 All subsets Hard
- Python 28 Spiral order Hard
- Python 29 Permutations by hand Hard
- Python 30 Round robin Hard
Logic
- Logic 1 Binary to decimal and back Easy
- Logic 2 Handshakes Easy
- Logic 3 Fence posts Easy
- Logic 4 Bat and ball Easy
- Logic 5 Lily pads Easy
- Logic 6 Counting in hex Easy
- Logic 7 Socks in the dark Easy
- Logic 8 Three switches, one bulb Easy
- Logic 9 Guess the number Easy
- Logic 10 Count the loop Easy
- Logic 11 Truth table mystery Easy
- Logic 12 Rank the Big-Os Easy
- Logic 13 De Morgan's laws Medium
- Logic 14 Burning ropes Medium
- Logic 15 Water jugs Medium
- Logic 16 Knights and knaves Medium
- Logic 17 Bit strings with three ones Medium
- Logic 18 100 lockers Medium
- Logic 19 Two guards, two doors Medium
- Logic 20 Counting recursive calls Medium
- Logic 21 Monty Hall Medium
- Logic 22 Find the heavy ball Medium
- Logic 23 Tower of Hanoi Medium
- Logic 24 The birthday paradox Medium
- Logic 25 The bridge at night Hard
- Logic 26 One poisoned bottle Hard
- Logic 27 Two eggs, 100 floors Hard
- Logic 28 The Josephus problem Hard
- Logic 29 25 horses Hard
- Logic 30 The hat line Hard
Data structures
- Data structures 1 Contains a duplicate Easy
- Data structures 2 Two sum Easy
- Data structures 3 Intersection of two lists Easy
- Data structures 4 The missing number Easy
- Data structures 5 Balanced brackets Easy
- Data structures 6 First unique character Easy
- Data structures 7 Binary search, by hand Easy
- Data structures 8 Merge two sorted lists Easy
- Data structures 9 Depth of a binary tree Easy
- Data structures 10 Middle of a linked list Easy
- Data structures 11 Insertion sort Easy
- Data structures 12 Best window sum Easy
- Data structures 13 Reverse a linked list Medium
- Data structures 14 Queue from two stacks Medium
- Data structures 15 Does the list loop? Medium
- Data structures 16 Group the anagrams Medium
- Data structures 17 Top k frequent Medium
- Data structures 18 Merge intervals Medium
- Data structures 19 Maximum subarray Medium
- Data structures 20 Product of everything else Medium
- Data structures 21 Min stack Medium
- Data structures 22 Level order traversal Medium
- Data structures 23 Longest substring without repeats Medium
- Data structures 24 Count the islands Medium
- Data structures 25 Build a trie Medium
- Data structures 26 Validate a binary search tree Hard
- Data structures 27 LRU cache Hard
- Data structures 28 Course schedule Hard
- Data structures 29 Shortest path in a grid Hard
- Data structures 30 Dijkstra's algorithm Hard