What is recursion and why is it dangerous?
The gist
Recursion is a function calling itself, reducing the problem to a smaller one. It needs a base case (stop condition) and a step that moves toward the base. It is natural for trees, graphs, divide and conquer (merge sort, quicksort), and parsing nested structures (JSON, expressions).
func sumTo(_ n: Int) -> Int { n == 0 ? 0 : n + sumTo(n - 1) }
print(sumTo(10_000)) // 50005000The rest of this answer, with code and interview follow-ups, is in the DevPrep app.
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