A binary tree’s **maximum depth** is the number of nodes along the longest path from the root node down to the farthest leaf node.

**Time Complexity:** O(N)

**Approach**,

**Implementation**,

`var maxDepth = function(root) {`

if (root === null) return 0

return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1

};

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