HomeLearn the Basics
Learn the Basics
Complexity, patterns, recursion and hashing — the foundation.
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- Time & Space ComplexityBig-O · how cost grows with inputanimatedEasy
- Recursion — the BasicsBase case + a smaller subproblemanimatedEasy
- Hashing — the BasicsO(1) average lookups, counts & setsanimatedEasy
- Loops & Number PatternsNested loops build rows and columnsanimatedEasy
- Practice problems
- Cpp BasicsHeaders, main(), input and outputEasy
- If ElseIfBranching on a conditionanimatedEasy
- Switch CaseOne value, many branchesanimatedEasy
- What are arrays, strings?Contiguous memory, 0-based indexinganimatedEasy
- For loopsRepeat a known number of timesanimatedEasy
- While loopsRepeat until a condition breaksanimatedEasy
- Functions (Pass by Reference and Value)Copies versus aliasesanimatedEasy
- Theory with examplesHow to approach any problemEasy
- Easy and MediumMixed warm-up setEasy
- Pattern 1Solid n x n squareanimatedEasy
- Pattern 2Left-aligned right triangleanimatedEasy
- Pattern 3Number triangle 1..i per rowanimatedEasy
- Pattern 4Row i repeats the number ianimatedEasy
- Pattern 5Inverted star triangleanimatedEasy
- Pattern 6Inverted number triangleanimatedEasy
- Pattern 7Centred star pyramidanimatedEasy
- Pattern 8Inverted centred pyramidanimatedEasy
- Pattern 9Star diamondanimatedEasy
- Pattern 10Star hill that grows then shrinksanimatedEasy
- Pattern 11Alternating 1/0 triangleanimatedEasy
- Pattern 12Number crown with a gapanimatedEasy
- Pattern 13Continuously increasing numbersanimatedEasy
- Pattern 14Alphabet triangle A, AB, ABCanimatedEasy
- Pattern 15Shrinking alphabet triangleanimatedEasy
- Pattern 16Row i repeats the i-th letteranimatedEasy
- Pattern 17Alphabet hill A, ABA, ABCBAanimatedEasy
- Pattern 18Triangle of trailing lettersanimatedEasy
- Pattern 19Star butterflyanimatedEasy
- Pattern 20Star butterfly, opening outwardanimatedMedium
- Pattern 21Hollow square outlineanimatedMedium
- Pattern 22Concentric number squareanimatedMedium
- STLC++ containers and algorithmsanimatedEasy
- Java CollectionsJava's equivalent toolboxanimatedEasy
- Count all Digits of a NumberDivide by 10 until nothing is leftanimatedEasy
- Reverse a numberPop digits off the back, push onto a new numberanimatedEasy
- Palindrome NumberReverse it and compareEasy
- GCD of Two NumbersEuclid: replace the larger with the remainderEasy
- Check if the Number is ArmstrongSum of digits raised to the digit countEasy
- Print all DivisorsOnly walk up to the square rootEasy
- Check for Prime NumberTrial division up to the square rootEasy