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BinaryTreeIters.java
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BinaryTreeIters.java
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import java.util.Iterator;
import java.util.Stack;
class Tree<E> {
public Tree(E v) {
this.v = v;
}
public Tree(Tree<E> l, E v, Tree<E> r) {
this.l = l;
this.v = v;
this.r = r;
}
public Tree<E> l = null;
public E v;
public Tree<E> r = null;
}
class PreOrderIter<E> implements Iterator<E> {
public PreOrderIter(Tree<E> n) {
stack.push(n);
}
public E next() {
Tree<E> n = stack.pop();
if (n.r != null) {
stack.push(n.r);
}
if (n.l != null) {
stack.push(n.l);
}
return n.v;
}
public boolean hasNext() {
return !stack.empty();
}
public void remove() {
throw new UnsupportedOperationException();
}
private Stack<Tree<E>> stack = new Stack<>();
}
class InOrderIter<E> implements Iterator<E> {
public InOrderIter(Tree<E> n) {
findLeft(n);
}
public E next() {
Tree<E> n = path.pop();
findLeft(n.r);
return n.v;
}
public boolean hasNext() {
return !path.empty();
}
public void remove() {
throw new UnsupportedOperationException();
}
private void findLeft(Tree<E> n) {
while (n != null) {
path.push(n);
n = n.l;
}
}
private Stack<Tree<E>> path = new Stack<>();
}
class PostOrderIter<E> implements Iterator<E> {
public PostOrderIter(Tree<E> n) {
findLeaf(n);
}
public E next() {
Tree<E> n = path.pop();
if (!path.empty()) {
Tree<E> p = path.peek();
if (p.l == n) {
findLeaf(p.r);
}
}
return n.v;
}
public boolean hasNext() {
return !path.empty();
}
public void remove() {
throw new UnsupportedOperationException();
}
private void findLeaf(Tree<E> n) {
while (n != null) {
path.push(n);
if (n.l != null) {
n = n.l;
} else {
n = n.r;
}
}
}
private Stack<Tree<E>> path = new Stack<>();
}
public class BinaryTreeIters {
private static Tree<Integer> tree(int v) {
return new Tree<>(v);
}
private static Tree<Integer> tree(Tree<Integer> l, int v, Tree<Integer> r) {
return new Tree<>(l, v, r);
}
public static void main(String[] args) {
Tree<Integer> t = tree(tree(tree(1), 2, tree(3)),
4,
tree(tree(5), 6, tree(7)));
Iterator<Integer> iter = new PreOrderIter<>(t);
while (iter.hasNext()) {
System.out.print(iter.next() + " ");
}
System.out.println();
iter = new InOrderIter<>(t);
while (iter.hasNext()) {
System.out.print(iter.next() + " ");
}
System.out.println();
iter = new PostOrderIter<>(t);
while (iter.hasNext()) {
System.out.print(iter.next() + " ");
}
System.out.println();
}
}