Recursion and iteration are both ways to repeat operations, but they work differently under the hood. Iteration uses loops (for, while) and keeps a single copy of the loop variables. Recursion uses function calls that pile up on the call stack, with each call holding its own set of variables.
Use Iteration When
- You are processing arrays, lists, or ranges linearly
- Performance and memory matter (recursion has function call overhead)
- The depth of processing is large (more than a few hundred levels)
- Your team will read the code later — loops are usually easier to understand
Use Recursion When
- You are working with tree-like data structures (file systems, DOM, JSON)
- The problem has a natural recursive definition (factorial, Fibonacci, but even these are better iteratively in practice)
- You need backtracking (sudoku solver, maze solving, N-Queens)
- You are using divide-and-conquer (merge sort, quick sort)
The Stack Overflow Trap
Every recursive call adds a frame to the call stack. If your recursion goes too deep, you hit a stack overflow. Most languages have a default stack limit of a few thousand calls. If your problem might go deep, always reach for iteration or use techniques like tail-call optimization (if your language supports it).
A Practical Rule of Thumb
If you can write a simple loop, write a loop. If the loop would need its own stack data structure to manage state, consider recursion. When in doubt, write the iterative version first. You can always refactor to recursion later if the code becomes clearer.
