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Tree Traversal and Recursive Structure Reasoning

Problem

When you see binary tree questions about height, validity, symmetry, traversal by level, or constructive recursion

Strategy: Tree Traversal and Recursive Structure Reasoning

  • Think about this
    • First classify:
      • compute from children -> DFS recursion
      • grouped by depth -> BFS with queue
      • BST validity -> pass ancestor bounds or inorder increasing
      • symmetry -> compare mirrored node pairs
      • build balanced tree from sorted array -> choose middle recursively
    • Trees are often easiest as recursive definitions.
  • Avoid this
    • Do not check BST using only parent-child comparisons.
    • Do not ignore None positions in symmetry/shape-sensitive problems.
    • Do not use list pop(0) for BFS.
    • Do not overfit to one exact tree shape when many valid outputs exist.
  • Tell this to the interviewer
    • Name the traversal choice and why:
      • DFS for subtree recurrence
      • BFS for level grouping
    • State the recursive contract clearly:
      • what the helper returns
      • what bounds/state it receives
  • See these problems