Asked at
Binary Tree Preorder Traversal
EasyVerifiedTreeDFSStack~12 min
Given the root of a binary tree, return the preorder traversal of its node values: node, then left subtree, then right subtree.
A node is { val, left, right } with null children; the whole empty tree is null. The input arrives as the root node directly.
Examples
in{val:1, right:{val:2, left:{val:3}}}
out[1, 2, 3]
Node, then left subtree, then right subtree, applied recursively.
innull
out[]
An empty tree yields no values.
Constraints
- 0 ≤ number of nodes ≤ 100
- -100 ≤ node.val ≤ 100
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