Think recursively. The depth of a tree is + the maximum depth of its subtrees. What's the depth of an empty tree? . What's the depth of a leaf node? . What's the depth of any other node? + max(left depth, right depth). This naturally leads to a recursive solution.
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$ curl repovive.com/roadmaps/maang-interview-prep/trees-bst/maximum-depth-of-binary-tree-hint
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