Opening scenario
Problem references use LC for LeetCode.
Invert a binary tree (LC 226): swap every node's left and right child and return the root. Then two follow-ups you should expect: Binary Tree Right Side View (LC 199) — return the values you'd see standing to the right of the tree, top to bottom; and Find Bottom Left Tree Value (LC 513) — return the leftmost value on the deepest level.
Nodes have val, left, and right fields. Inversion and right-side view allow an empty tree; bottom-left value assumes at least one node. Begin by deciding whether the answer depends on child subtrees or on complete levels.
Question progression
Q1 — Invert asks you to touch every node. What is the smallest correct recursion?
Question: To invert, what must happen at a single node, and how do you know the whole tree is handled?
Reasoning: At one node the job is local: swap…
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In the full tutorial
- Canonical Template
- Complexity
- Pattern Recognition Signals
- Practice Set
- Pitfalls
- Variations
- Closing: When to Reach for This