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OldTreeIterator.java
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OldTreeIterator.java
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import java.util.Deque;
import java.util.Iterator;
import java.util.LinkedList;
public class treeIterator implements Iterator {
private Deque<TreeNode> stack;
private TreeNode cur;
private TreeNode pre; // only used in post order
private Type type;
public treeIterator(TreeNode root, Type type) { //suppose root != null
this.stack = new LinkedList<>();
this.type = type;
switch (type) {
case preOrder:
stack.addFirst(root);
break;
case inOder:
case postOrder:
//go all the way to the most left
cur = root;
while(cur != null) {
stack.addFirst(cur);
pre = cur;
cur = cur.left;
}
break;
}
}
@Override
public boolean hasNext() {
return stack.size() != 0;
// return cur != null;
}
@Override
public Integer next() {
if(stack.isEmpty()) {
return null;
}
else {
switch (type) {
case preOrder:
cur = stack.removeFirst();
if (cur.right != null) {
stack.addFirst(cur.right);
}
if (cur.left != null) {
stack.addFirst(cur.left);
}
return cur.key;
case inOder:
Integer retval = null;
do {
if (cur != null) {
stack.addFirst(cur);
cur = cur.left;
} else {
cur = stack.removeFirst();
retval = cur.key;
cur = cur.right;
}
} while (cur != null);
return retval;
case postOrder:
while (true) {
cur = stack.peekFirst();
if (pre.left == cur || pre.right == cur) {
pre = cur;
if (cur.left != null) {
stack.addFirst(cur.left);
} else if (cur.right != null) {
stack.addFirst(cur.right);
} else {
stack.removeFirst();
return cur.key;
}
}
else if (cur.left == pre) {
pre = cur;
if (cur.right != null) {
stack.addFirst(cur.right);
} else {
stack.removeFirst();
return cur.key;
}
}
else {
pre = cur;
stack.removeFirst();
return cur.key;
}
}
}
return null;
}
}
public static void main(String[] args) {
TreeNode tr3 = new TreeNode(3);
tr3.left = new TreeNode(1);
tr3.right = new TreeNode(4);
TreeNode tr8 = new TreeNode(8);
tr8.right = new TreeNode(11);
TreeNode root = new TreeNode(5);
root.left = tr3;
root.right = tr8;
TreeIterator1 iter = TreeIteratorFactory.getTreeIterator(root, IteratorType.POSTORDER);
while (iter.hasNext()) {
System.out.println(iter.next());
}
}
}
class TreeNode {
Integer key;
TreeNode left;
TreeNode right;
public TreeNode(int key) {
this.key = key;
this.left = null;
this.right = null;
}
}
enum Type {
inOder, preOrder, postOrder
}