Recursion & DP medium time O(2ⁿ) space O(n)
Recursion — Fibonacci Call Tree
Plain recursive Fibonacci calls itself twice per node, so the call tree branches exponentially. Identical subtrees appear over and over — the same f(2) is computed from scratch several times. That repeated work is exactly what memoisation and DP remove.
Compute f(5) by plain recursion — every call spawns two more.
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A fixed scene — scrub through it, or open the code.
Practice
Machine twin: /dsa-viz-v2/recursion-fibonacci.json — the full deterministic run as structured data.