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Unformatted text preview: CSCI1200 Data Structures Fall 2010 Lecture 18 Trees, Part III Review from Lecture 17 Implementing ds set operations: insert, destroy, printing, erase Todays Lecture Adding parent pointers, insert & erase w/ parent pointers Increment and decrement operations on iterators Limitations of our implementation, brief intro to redblack trees 18.1 Tree Height, Longest & Shortest Paths (From last lecture... ) The height of a node in a tree is the length of the longest path down the tree from that node to a leaf node. The height of a leaf is therefore 0. We will think of the height of a null pointer as 1. The height of the tree is the height of the root node, and therefore if the tree is empty the height will be 1. An exercise from last lecture was to write a simple recursive algorithm to calculate the height of a tree. Lets write it now. What is the running time of this algorithm? Now lets write a function to calculate the shortest path to a NULL child pointer. What is the running time of this algorithm? Can we do better? 18.2 Tree Iterators (review and with more detail) The increment operator should change the iterators pointer to point to the next TreeNode in an inorder traversal the inorder successor while the decrement operator should change the iterators pointer to point to the inorder predecessor. Unlike the situation with lists and vectors, these predecessors and successors are not necessarily nearby (either in physical memory or by following a link) in the tree, as examples we draw in class will illustrate. There are two common solution approaches: Each iterator maintains a stack of pointers representing the path down the tree to the current node. Each node stores a parent pointer. Only the root node has a null parent pointer. Lets go with the parent pointer method. Most of the changes are simple, but we need to revise the implemen tation of several member functions, including insert and erase , to correctly adjust parent pointers. See the attached source code. 18.3 Erase (now with parent pointers) (Review from last lecture... ) First we need to find the node to remove.(Review from last lecture....
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 Fall '08
 CUTLER
 Data Structures

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