# In-Order Traversals

###### In-Order Traversals
ECE 250 Algorithms and Data Structures InOrder Traversals Douglas Wilhelm Harder, M.Math. LEL Department of Electrical and Computer Engineering University of Waterloo Waterloo, Ontario, Canada ece.uwaterloo.ca dwharderalumni.uwaterloo.ca © 20062013 by Douglas Wilhelm Harder. Some rights reserved.Inorder traversals 2 Outline In this topic we will look at: – Inorder traversals of binary search trees – Limitations of inorder traversals with nary treesInorder traversals 3 4.11.1 Inorder Traversals We’ve seen two depthfirst traversals: – Preorder – Postorder First and last visits during an Euler walkInorder traversals 4 4.11.1 Inorder Traversals For binary trees, there is a third intermediate visit – An inorder depthfirst traversalInorder traversals 5 4.11.1 Inorder Traversals This visits a binary search tree in order A, B, C, D, E, F, G, H, I, JInorder traversals 6 Application An implementation of an inorder traversal template typename Type void BinarytreeType::inordertraversal() const if ( empty() ) return; left()inordertraversal(); cout retrieve(); right()inordertraversal(); Inorder traversals 7 4.11.1.1 Inorder traversals on expression trees Printing an expression tree (pretty printing or humanreadable printing) using infix notation requires an inorder traversal (3x + 5 + y)(z + 7)Inorder traversals 8 Application class Expressionnode; void Expressionnode::prettyprint() if ( leaf() ) // If the precedence of the parent is higher than that of the // current operator, we need to print an opening parenthesis if ( parent()precedence() precedence() ) cout "("; // preorder visit left()prettyprint(); // traverse left tree // The inorder step: print this object cout this; // print this objectInorder traversals 9 Application if ( leaf() ) right()prettyprint(); // traverse right subtree // If the precedence of the parent is higher than that of the // current operator, we need to print a closing parenthesis if ( parent()precedence() precedence() ) cout ")"; // postorder visit Inorder traversals 10 4.11.1.3 Inorder traversals on general trees An inorder traversal does not make sense for either general trees or Nary trees with N 2Inorder traversals 11 Summary In this topic, we have looked at: – Inorder depthfirst traversals – Limitations on Nary and binary treesInorder traversals 12 References 1 Cormen, Leiserson, and Rivest, Introduction to Algorithms, MIT Press, 1990, §7.13, p.152. rd 2 Weiss, Data Structures and Algorithm Analysis in C++, 3 Ed., Addison Wesley, §6.56, p.21525.Inorder traversals 13 Usage Notes • These slides are made publicly available on the web for anyone to use • If you choose to use them, or a part thereof, for a course at another institution, I ask only three things: – that you inform me that you are using the slides, – that you acknowledge my work, and – that you alert me of any mistakes which I made or changes which you make, and allow me the option of incorporating such changes (with an acknowledgment) in my set of slides Sincerely, Douglas Wilhelm Harder, MMath dwharderalumni.uwaterloo.ca
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