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DSA · interactive

Trees: let the children answer first

Most tree problems have the same shape: ask the left child, ask the right child, then combine their answers. Watch it find the depth of a tree, one call at a time.

Step 1 of 15

running nowwaiting on the stackanswer returned
4251637

Call stack

  1. maxDepth(1)

Height now 1. Tallest it gets: 3, the depth of the tree.

maxDepth(1) is called. Before it can answer, it has to ask its children.

Tree

1 of 7 calls
  1. 1

    maxDepth(node) is a question: how many levels are there from this node down? The call goes on the stack and waits.

    maxDepth(1) is waiting

  2. 2

  3. 3

  4. 4

Now solve it

Trees: 13 problems

See all →

In production

Tools and technologies

Trees are everywhere software keeps a hierarchy, and most code that walks them is this same recursion.

Not tied to one language — use these names when you search docs or design a system.