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Concept

Passing Values Down and Up

Parameters go down, returns come up
step 1 / 18
binary tree
4
2
1
3
5
call stack ↓
(returned)
Concept
▸
1walk(node, depth):                  // depth PASSED DOWN ↓
2    push frame
3    if node is null: return depth-1     // base case
4    return max(depth,                   // RETURN max depth UP ↑
5               walk(node.left,  depth+1),
6               walk(node.right, depth+1))
state
  • ↓ paramdepth
  • ↑ returnmax depth

line 1Recursion moves data in TWO directions. Parameters carry context DOWN from parent to child; return values carry answers UP from child to parent. We will compute each node's depth (passed DOWN) and the tree's maximum depth (returned UP) in a single walk.