🔄 Think of Recursion Like Stack Frames

When you call a function in Python, it gets added to a call stack.

• The current function is paused while waiting for the recursive call to finish.
• Once the recursive call returns, the paused function resumes and finishes.

📦 Real-Life Analogy: Stack of Tasks

Imagine you're unpacking boxes, and each box has another box inside:

1. Open Box 1 → inside is Box 2
2. Open Box 2 → inside is Box 3
3. Open Box 3 → it's empty
4. Now close Box 3, then Box 2, then Box 1 (in reverse)

🧠 This is Last In, First Out (LIFO) — like a stack.

🧠 Recursive Tree Example

Let’s use a very small tree to understand it fully:

markdown
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    1
   / \\
  2   3

Now let’s run your function dfs() on this tree.

🔁 Visualizing Recursive Calls

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dfs(1)
├── dfs(2)
│   ├── dfs(None) → 0
│   └── dfs(None) → 0
│   return 1 + max(0, 0) = 1
├── dfs(3)
│   ├── dfs(None) → 0
│   └── dfs(None) → 0
│   return 1 + max(0, 0) = 1
return 1 + max(1, 1) = 2