1. Base case
The smallest input answered directly, with no further calls.
if (n <= 1)Typorithm · easy
Recursion Basics
recursion-basicspatternsbase-casecall-stack
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Full lesson · 8 learning steps Open any exercise for focused practice
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Step 1 of 8 · intro card
Learn Recursion Basics
Basic Patterns
Recursion solves a problem by combining the answer to a smaller version of itself.
Every recursive function needs a base case that returns without recursing.
The recursive step must shrink the input toward that base case.
Each call waits on the stack until the smaller call returns its answer.
01
Base case first, always.
02
Shrink the input every call.
03
Trust the smaller call's answer.
function factorial(n) {
if (n <= 1) {
return 1;
}
return n * factorial(n - 1);
}Read the implementation
Connect each part of the code to the concept before you type.
2. Base value
factorial(1) and factorial(0) are both 1 by definition.
return 13. Recursive step
Combine the current value with the answer for a smaller input.
return n * factorial(n - 1)A complete learning loop
01
Understand
Read the concept map and follow the code breakdown.
02
Reconstruct
Type the implementation, repair mistakes and work through every recall exercise.
03
Verify
Use the final check without hints; revisit weak concepts in short practice sessions.