Binary Tree Inorder Traversal in Java: Explanation & Practice

Problem summary

Given a binary tree, return the inorder traversal of its nodes' values. Implement iteratively using a stack.

Starter code

public class Main {
    public static void main(String[] args) {
        // Tree:   1
        //          \
        //           2
        //          /
        //         3
        // Inorder: Left, Root, Right
        // Print: 1 3 2
    }
}

Expected output and test cases

• [1,null,2,3]

  1 3 2

• [] → empty

• [1]

  1

Hints

1. Recursive: inorder(left), visit root, inorder(right)
2. Iterative: use stack, go left as far as possible
3. Pop node, add to result, then go right
4. Repeat until stack empty and current is null

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