6.18 Revise the algorithm of Figure 6.6 so that it performs an in-order enumeration, rather than preorder. class BinTree implements Iterable { BinTree left: BinTree right; T val; } *** // other methods: insert, delete, lookup, public Iterator iterator () { return new TreeIterator (this); } private class TreeIterator implements Iterator { private Stack> a= new Stack>(); TreeIterator (BinTree n) { if (n. val - null) s.push (n); } } public boolean hasNext() { return s. empty(); } public T next() { if (!has Next ()) throw new NoSuchElementException(); BinTree n = s.pop(); if (n.right != null) s.push(n.right); if (n.left= null) s.push(n.left); return n. val; } public void remove() { throw new Unsupported OperationException(); } Figure 6.6 Java code for preorder enumeration of the nodes of a binary tree. The nested TreeIterator class uses an explicit Stack object (borrowed from the standard library) to keep track of subtrees whose nodes have yet to be enumerated. Java generics, specified as type arguments for BinTree, Stack, Iterator, and Iterable, allow next to return an object of the appropriate type, rather than the undifferentiated Object. The remove method is part of the Iterator interface, and must therefore be provided, if only as a placeholder.
6.18 Revise the algorithm of Figure 6.6 so that it performs an in-order enumeration, rather than preorder. class BinTree implements Iterable { BinTree left: BinTree right; T val; } *** // other methods: insert, delete, lookup, public Iterator iterator () { return new TreeIterator (this); } private class TreeIterator implements Iterator { private Stack> a= new Stack>(); TreeIterator (BinTree n) { if (n. val - null) s.push (n); } } public boolean hasNext() { return s. empty(); } public T next() { if (!has Next ()) throw new NoSuchElementException(); BinTree n = s.pop(); if (n.right != null) s.push(n.right); if (n.left= null) s.push(n.left); return n. val; } public void remove() { throw new Unsupported OperationException(); } Figure 6.6 Java code for preorder enumeration of the nodes of a binary tree. The nested TreeIterator class uses an explicit Stack object (borrowed from the standard library) to keep track of subtrees whose nodes have yet to be enumerated. Java generics, specified as type arguments for BinTree, Stack, Iterator, and Iterable, allow next to return an object of the appropriate type, rather than the undifferentiated Object. The remove method is part of the Iterator interface, and must therefore be provided, if only as a placeholder.
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
Problem 1PE
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Please help me with this Principles of programming language homework question
Transcribed Image Text:6.18 Revise the algorithm of Figure 6.6 so that it performs an in-order enumeration, rather than
preorder.
class BinTree<T> implements Iterable<T> {
BinTree<T> left:
BinTree<T> right;
T val;
***
// other methods: insert, delete, lookup, ...
public Iterator<T> iterator () {
return new TreeIterator (this);
}
private class TreeIterator implements Iterator<T> {
private Stack<BinTree<T>> s= new Stack<BinTree<T>>();
TreeIterator (BinTree<T> n) {
if (n.val != null) s.push (n);
}
}
public boolean hasNext () {
return s. empty ();
}
public T next () {
if (!hasNext()) throw new NoSuchElementException();
BinTree<T> n = s.pop();
if (n.right != null) s.push (n.right);
if (n.left != null) s.push(n.left);
return n. val;
}
public void remove() {
throw new Unsupported OperationException();
}
}
Figure 6.6 Java code for preorder enumeration of the nodes of a binary tree. The nested
TreeIterator class uses an explicit Stack object (borrowed from the standard library) to keep
track of subtrees whose nodes have yet to be enumerated. Java generics, specified as <T> type
arguments for BinTree, Stack, Iterator, and Iterable, allow next to return an object of
the appropriate type, rather than the undifferentiated Object. The remove method is part of
the Iterator interface, and must therefore be provided, if only as a placeholder.
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