Yosgi Siqi Liu

Pruning subtrees that contain no 1 with post-order traversal, using a dummy parent so the root can also be pruned.

Summing all root-to-leaf numbers with top-down pre-order DFS, carrying the running value down each path.

Computing the total tilt of a binary tree with recursion that returns each subtree's sum.

Counting paths with a target sum starting from any node, using an outer recursion over nodes and an inner recursion over paths.

Finding the maximum path sum in a binary tree with recursion that returns each node's best downward contribution.

Counting nodes in a complete binary tree using left/right subtree depths instead of a full DFS.

Computing the maximum width of a binary tree with BFS, tracking each node's position index within its level.

Finding all nodes at distance K by first adding parent links with DFS, then searching outward from the target.

Validating a binary search tree by exploiting the increasing order of its in-order traversal.

Restoring a BST with two swapped nodes by locating them during an in-order traversal.