Recursion vs Iteration

Call Stack · Tail Calls · Conversion

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What really separates recursion from iteration — call-stack cost, tail calls, TCO language support, and when to convert between the two.

By the end, you can

Explain the difference between the recursive and iterative models for the same algorithm.
Trace how the call stack grows and unwinds for a small recursive call (e.g. `factorial(5)`), counting the peak number of live frames.
State the space complexity of each approach and explain why an in-place loop is O(1) while recursion is O(depth).
Identify a tail call and rewrite a non-tail recursive function using an accumulator to make it tail-recursive.
List which languages/runtimes guarantee tail-call elimination and which do not (including the Python 3.14 myth).
Convert a recursive function to an iterative one using an explicit stack, and vice versa using an accumulator.
Choose between recursion and iteration given a problem description and constraints.

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