juniorFibonacci Series
What is the time complexity of the naive recursive Fibonacci?
Updated Apr 28, 2026
Short answer
O(2^n) because of the exponential growth of the recursion tree.
Deep explanation
The Fibonacci sequence is defined by the recurrence relation $F_n = F_{n-1} + F_{n-2}$. O(2^n) because of the exponential growth of the recursion tree.
Real-world example
Modeling population growth in ideal conditions.
Common mistakes
- Using a 1-based index when the interviewer expects 0-based.
Follow-up questions
- What is the 5th Fibonacci number?