Why is the naive Fibonacci sequence O(2^N)?
Because every function call spawns exactly two more function calls, causing the total number of operations to double at every level of depth.
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More FAQs in Understanding the Recursion Tree Method
A Recursion Tree is a visual diagram where each node represents a function call, and the branches represent the subsequent recursive calls made from that function.
You sum up the amount of non-recursive work done across all nodes at every level of the tree.
You use Dynamic Programming (Memoization). By caching the result of a node, you prevent the tree from recalculating overlapping branches, collapsing O(2^N) into O(N).
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