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Comp202: Principles of Object-Oriented Programming II
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Consider the following binary tree.
1
/
\
2
3
/ \
\
4 5
6
/
7
The breadth first traversal from left to right consists of visiting the nodes: 1, 2, 3, 4, 5, 6, 7 in this order. To traverse the tree in this manner, each time we visit a non-empty node, we need to save its two children in a FIFO queue, process the current node, then go through the queue and process each node in the queue in the same manner. Here is the code for printing a tree in breadth-first order.
package brs.visitor;
import brs.*; import rac.*;
/**
* Prints the tree nodes in breadth traversal.
* Uses a FIFO queue.
* @author DXN
*/
public class BreadthPrint implements IVisitor {
private IRAContainer _queue = new LRSQueueFactory().makeRAC();
// IRAContainer visitor to go through the queue and process each tree
// in the queus with a given BiTree visitor.
private IRACVisitor _processQ = new IRACVisitor() {
public Object emptyCase(IRAContainer q, Object treeVis) {
return null;
}
public Object nonEmptyCase(IRAContainer q, Object treeVis) {
((BiTree)q.get()).execute((IVisitor)treeVis, null);
return q.execute(this, treeVis);
}
};
/**
* Nothing to print here.
*/
public Object emptyCase(BiTree host, Object nu) {
return null;
}
/**
* Prints the root data, saves the left and right subtrees in _queue
* and "process" _queue.
*/
public Object nonEmptyCase(BiTree host, Object nu) {
_queue.put(host.getLeftSubTree());
_queue.put(host.getRightSubTree());
System.out.print(host.getRootDat());
return _queue.execute(_processQ, new IVisitor() {
public Object emptyCase(BiTree h, Object nu) {
return null;
}
public Object nonEmptyCase(final BiTree h, Object nu) {
_queue.put(h.getLeftSubTree());
_queue.put(h.getRightSubTree());
System.out.print(" " + h.getRootDat());
return null;
}
});
}
/**
* Simple test code.
*/
public static void main(String[] args) {
BiTree t0 = new BiTree();
t0.insertRoot(new Integer(1));
BiTree t1 = new BiTree();
t1.insertRoot(new Integer(2));
BiTree t2 = new BiTree();
t2.insertRoot(new Integer(3));
t0.setLeftSubTree(t1);
t0.setRightSubTree(t2);
t1.getLeftSubTree().insertRoot(new Integer(4));
t1.getLeftSubTree().getRightSubTree().insertRoot(new Integer(6));
t2.getRightSubTree().insertRoot(new Integer(5));
t2.getRightSubTree().getLeftSubTree().insertRoot(new Integer(7));
System.out.println("t0 is: \n" + t0 + "\n");
System.out.println("Breadth first traversal:");
t0.execute(new BreadthPrint(), null);
System.out.println("\nDone!");
}
}
What is the abstract processing here? Use a lambda where you see System.out.println. Here is the code for the invariant breadth-first tree traversal, where the variant is simply a lambda.
package brs.visitor;
import brs.*; import rac.*; import fp.*;
/**
* Processes the tree nodes via breadth-first traversal.
* Uses a FIFO queue.
* @author DXN
*/
public class BreadthFirst implements IVisitor {
private IRAContainer _queue = new LRSQueueFactory().makeRAC();
private ILambda _f;
private Object _acc; // accumulated result.
// IRAContainer visitor to go through the queue and process each tree
// in the queus with a given BiTree visitor.
private IRACVisitor _processQ = new IRACVisitor() {
public Object emptyCase(IRAContainer q, Object treeVis) {
return _acc;
}
public Object nonEmptyCase(IRAContainer q, Object treeVis) {
((BiTree)q.get()).execute((IVisitor)treeVis, null);
return q.execute(this, treeVis);
}
};
public BreadthFirst(ILambda f) {
_f = f;
}
/**
*/
public Object emptyCase(BiTree host, Object b) {
return b;
}
/**
* Processes the root data, saves the left and right subtrees in _queue
* and "process" _queue.
*/
public Object nonEmptyCase(BiTree host, final Object b) {
_queue.put(host.getLeftSubTree());
_queue.put(host.getRightSubTree());
_acc = _f.apply(host, b);
return _queue.execute(_processQ, new IVisitor() {
public Object emptyCase(BiTree h, Object nu) {
return b; // anything, _acc ok too.
}
public Object nonEmptyCase(final BiTree h, Object nu) {
_queue.put(h.getLeftSubTree());
_queue.put(h.getRightSubTree());
_acc = _f.apply(h, _acc);
return _acc;
}
});
}
/**
* Simple test code.
*/
public static void main(String[] args) {
BiTree t0 = new BiTree();
t0.insertRoot(new Integer(1));
BiTree t1 = new BiTree();
t1.insertRoot(new Integer(2));
BiTree t2 = new BiTree();
t2.insertRoot(new Integer(3));
t0.setLeftSubTree(t1);
t0.setRightSubTree(t2);
t1.getLeftSubTree().insertRoot(new Integer(4));
t1.getLeftSubTree().getRightSubTree().insertRoot(new Integer(6));
t2.getRightSubTree().insertRoot(new Integer(5));
t2.getRightSubTree().getLeftSubTree().insertRoot(new Integer(7));
System.out.println("t0 is: \n" + t0 + "\n");
System.out.println("Breadth first printing:");
ILambda print = new ILambda() {
public Object apply(Object... args) {
System.out.print("" + args[1] + ((BiTree)args[0]).getRootDat());
return " ";
}
};
t0.execute(new BreadthFirst(print), "");
System.out.println("\nBreadth first adding:");
ILambda add= new ILambda() {
public Object apply(Object... args) {
return (Integer)args[1] + (Integer)((BiTree)args[0]).getRootDat();
}
};
System.out.println(t0.execute(new BreadthFirst(add), 0));
System.out.println("\nDone!");
}
}
Last Revised Thursday, 03-Jun-2010 09:52:33 CDT
©2007 Stephen Wong and Dung Nguyen