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CoursesTrees & Graphs

Tree DFS

Lessons
9
Exercises
57
Minutes
61
  1. 1

    Go Deep First

    Recursion mirrors the tree: dive to a leaf, let null stop you, and combine what the children return.

    Complete codeMultiple choiceTap
    6 exercises
    5 min
  2. 2

    Invert Binary Tree

    One swap per node — recursion carries it to every corner of the tree.

    Complete codeMultiple choiceTrace
    6 exercises
    6 min
  3. 3

    Path Sum

    Subtract as you descend — and remember that only a leaf can finish the path.

    Complete codeDebugMultiple choiceTrace
    7 exercises
    7 min
  4. 4

    Diameter of Binary Tree

    One recursion, two quantities: each node's best path is leftHeight + rightHeight, but the function must hand its parent a height.

    Complete codeDebugMultiple choiceTrace
    6 exercises
    7 min
  5. 5

    LCA of a BST

    BST ordering turns LCA into a single walk: both smaller go left, both larger go right, and the split point is the answer.

    Complete codeMultiple choiceTrace
    6 exercises
    6 min
  6. 6

    Kth Smallest in a BST

    Inorder traversal of a BST visits values in sorted order — count the visits and stop the recursion at the kth.

    Complete codeDebugMultiple choiceTrace
    6 exercises
    7 min
  7. 7

    Tree DFS CheckpointCheckpoint

    No new concepts — transfer the island's DFS moves to unseen trees: walking two trees at once, carrying path state down, and summing subtrees bottom-up.

    Complete codeCode orderMultiple choiceTrace
    6 exercises
    7 min
  8. 8

    Tree DFS ReviewReview

    Mixed recap of the island: state flowing down vs answers flowing up, BST ordering shortcuts, picking a traversal order, base cases, and the price of recomputing heights.

    Complete codeMultiple choiceTrace
    6 exercises
    6 min
  9. 9

    Boss: Validate Binary Search TreeBoss

    The island's final test: prove a tree is a BST. Every node must respect bounds set by ALL of its ancestors — checking children against parents is the trap. Carry (lo, hi) down, or verify the inorder walk climbs strictly.

    Complete codeDebugCode orderMultiple choiceTrace
    8 exercises
    10 min
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