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import java.util.ArrayList;
import java.util.List;
import java.util.Stack;

public class BinaryTraversal {

/**
* Definition for a binary tree node.
**/
public class TreeNode {
int val;
TreeNode left;
TreeNode right;

TreeNode(int x) {
val = x;
}
}

private static List<Integer> inOrder(TreeNode root) {
if(root == null) {
return new ArrayList<>();
}

List<Integer> result = new ArrayList<>();
Stack<TreeNode> s = new Stack<>();

TreeNode t = root;
while (t != null || !s.empty()) {
// find left most
if(t != null) {
s.push(t);
t = t.left;
}
else {
t = s.pop();
result.add(t.val);
t = t.right;
}
}
return result;
}

private static List<Integer> preOrder(TreeNode root) {
if(root == null) {
return new ArrayList<>();
}

List<Integer> result = new ArrayList<>();
Stack<TreeNode> s = new Stack<>();

TreeNode t = root;
while (t != null || !s.empty()) {
// find left most
if(t != null) {
s.push(t);
result.add(t.val);
t = t.left;
}
else {
t = s.pop();
t = t.right;
}
}
return result;
}

private static List<Integer> postOrder(TreeNode root) {
List<Integer> result = new ArrayList<>();
Stack<TreeNode> s = new Stack<>();
TreeNode t = root;
while (t != null || !s.empty()) {
if(t != null) {
if(t.right != null) {
s.push(t.right);
}
s.push(t);
t = t.left;
continue;
}

t = s.pop();
if(!s.empty() && t.right == s.peek()) {
TreeNode tmp = s.pop();
s.push(t);
t = tmp;
}
else {
result.add(t.val);
t = null;
}

}
return result;
}
}