Summary

A tree is a hierarchical structure of nodes connected by edges. The top is the root. A parent links to its children. A leaf has no children. depth counts steps from the root. height is the longest path down. A subtree is any node with its descendants. A binary_tree has up to two children. A binary_search_tree keeps left keys smaller and right keys larger. Common traversals: preorder, inorder, postorder, and bfs/dfs.