Binary Tree Traversal Methods Preorder Inorder In a traversal - PDF document

Binary Tree Traversal Methods Binary Tree Traversal Methods • Preorder • Inorder • In a traversal of a binary tree, each element of • Postorder the binary tree is visited exactly once. • Level order • During the visit of an element, all action (make a clone, display, evaluate the operator, etc.) with respect to this element is taken. Preorder Traversal Preorder Example (visit = print) public static void preOrder(BinaryTreeNode t) a { if (t != null) b c { visit(t); a b c preOrder(t.leftChild); preOrder(t.rightChild); } } Preorder Example (visit = print) Preorder Of Expression Tree / a * + b c e f f + - e d a b c j d g h i / * + a b - c d + e f a b d g h e i c f j Gives prefix form of expression!

Inorder Traversal Inorder Example (visit = print) public static void inOrder(BinaryTreeNode t) a { if (t != null) b c { inOrder(t.leftChild); b a c visit(t); inOrder(t.rightChild); } } Inorder Example (visit = print) Inorder By Projection (Squishing) a a b c b c f f e e d d j j g g h i h i g d h b e i a f j c g d h b e i a j c f Postorder Traversal Inorder Of Expression Tree public static void postOrder(BinaryTreeNode t) / { if (t != null) * + { e f postOrder(t.leftChild); + - postOrder(t.rightChild); a b c d visit(t); } a + b * c - d / e + f } Gives infix form of expression (sans parentheses)!

Postorder Example (visit = print) Postorder Example (visit = print) a a b c b c f e d b c a j g h i g h d i e b j f c a Traversal Applications Postorder Of Expression Tree a / b c * + f e f e d + - j g h i a b c d • Make a clone. a b + c d - * e f + / • Determine height. Gives postfix form of expression! •Determine number of nodes. Level Order Level-Order Example (visit = print) a Let t be the tree root. while (t != null) b c { f visit t and put its children on a FIFO queue; e d remove a node from the FIFO queue and j g h i call it t; // remove returns null when queue is empty } a b c d e f g h i j

Some Examples Binary Tree Construction preorder a a = ab • Suppose that the elements in a binary tree b b are distinct. b a • Can you construct the binary tree from inorder which a given traversal sequence came? = ab a b • When a traversal sequence has more than one element, the binary tree is not uniquely b b postorder defined. = ab a a • Therefore, the tree from which the sequence was obtained cannot be reconstructed a a level order uniquely. = ab b b Preorder And Postorder Binary Tree Construction preorder = ab a a b b postorder = ba • Can you construct the binary tree, given two traversal sequences? • Preorder and postorder do not uniquely define a • Depends on which two sequences are binary tree. given. • Nor do preorder and level order (same example). • Nor do postorder and level order (same example). Inorder And Preorder Inorder And Preorder a • inorder = g d h b e i a f j c • preorder = a b d g h e i c f j gdhbei fjc • Scan the preorder left to right using the • preorder = a b d g h e i c f j inorder to separate left and right subtrees. • a is the root of the tree; gdhbei are in the left • b is the next root; gdh are in the left subtree; fjc are in the right subtree. subtree; ei are in the right subtree. a a b fjc gdhbei fjc gdh ei

Inorder And Preorder Inorder And Postorder a b fjc • Scan postorder from right to left using gdh ei inorder to separate left and right subtrees. • preorder = a b d g h e i c f j • inorder = g d h b e i a f j c • d is the next root; g is in the left subtree; h is in the right subtree. • postorder = g h d i e b j f c a a • Tree root is a; gdhbei are in left subtree; fjc b fjc are in right subtree. d ei g h Inorder And Level Order • Scan level order from left to right using inorder to separate left and right subtrees. • inorder = g d h b e i a f j c • level order = a b c d e f g h i j • Tree root is a; gdhbei are in left subtree; fjc are in right subtree.