MediumVery High Frequency25 min
Recursion
Master the recursive thinking model — base cases, recurrence, and the call stack.
Recursion solves a problem by breaking it into smaller instances of itself. Every recursive solution needs a base case and a recursive case.
Recursion
Patterns
Power: x^n (Divide & Conquer)
O(log n)Naive loop is O(n). Recursion halves the problem → O(log n).Step-by-step1 / 3
Input stream
Invariant
Push work onto the stack; pop when the current token or base case resolves it.
Stacktop
myPow(2, 10)
half(2,5)
myPow(2, 10). Even: half(2,5)²
10 is even. Compute 2^5 once, square it.