Codility Lessons: solutions

Notes on doing each exercise

Read the "Open reading material (PDF)", currently at the top of each lesson. It gives you information needed to solve the exercises for the lesson. Some questions don't rely on information from the open reading material.
You don't need to test for cases outside of the given assumptions.
Each exercise has some basic tests, you can write your own test cases.
Performance matters. Consider the time complexity of your solutions. Be careful of nested loops!
You can estimate the expected time complexity of the solution based on the maximum size of the inputs:
- n =< 1 000 000, the expected time complexity is O(n) or O(n log n) - linear or logarithmic - no nested loops
- n =< 10 000, the expected time complexity is O(n2) - quadratic - nested loops
- n =< 500, the expected time complexity is O(n3) - cubic - nested nested loops
You can read more about time complexity in the open reading material for Lesson 3: Time Complexity.