Binary Tree Tree for which every node has at most 2 child nodes.
Binary Search Trees Invariant: For every node x the values in the left subtree are less or equal to x and the nodes in the right subtrees are greater or equal to x, x being the root.
Storing Rooted Trees Always maintain a pointer to the root.Each node has access to all of its children. Maintain a pointer to the parent node to make reverse traversal easy. - this isn't necessary thanks to recursive calls.
It can thus be represented as an array. This also works for n-array trees. The root is always index 0. For the children: left child = 2i+1 right child = 2i+2 parent = Floor((i-1)/2)
Height of a tree The number of edges from the root to the lowest leaf.