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Same Tree – Solution & Complexity

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Same Tree

1. Recognize the Pattern

The key pattern is: Parallel DFS compares corresponding nodes. Identify the state and invariant before coding.

2. Build the Algorithm

Advance one state transition at a time. Mark or update state before exploring dependent work.

3. Check Edge Cases

Test empty or minimal input, skewed shapes, duplicates where allowed, and impossible outcomes.

4. Solution and Complexity

Time: O(n). Space: O(h).

def is_same_tree(p: TreeNode, q: TreeNode) -> bool:
    if p is None or q is None:
        return p is q
    return p.val == q.val and is_same_tree(p.left, q.left) and is_same_tree(p.right, q.right)

FAQ

See also

Practice Same Tree online (run code in the browser)Invert Binary Tree solution (easy)Maximum Depth of Binary Tree solution (easy)Lowest Common Ancestor of a BST solution (medium)Validate Binary Search Tree solution (medium)All coding interview problems
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