[Interview type questions] First pair non matching leaves

Input: Given two (binary) trees, return the first pair of non-matching leaves Tree 1: A, B, C, D, E, null, null Tree 2: A, D, B
Output: (E,B)

Example:
Tree1 :              
      A
     /   \
   B     C
  /  \
D    E    

Tree2 :
    A
  /    \
D     B

Solution:

 static class TreeNode {
  public TreeNode(char v) { val = v;}
  char val;
  TreeNode left;
  TreeNode right;
 }
 
 static class MyIterator {
  Stack<TreeNode> stack = new Stack<>();
  MyIterator(TreeNode root) {
   pullAll(root);
  }
  
  void pullAll(TreeNode node) {
   while(node != null) {
    stack.push(node);
    node = node.left;
   }
  }
  
  public TreeNode next() {
   TreeNode next = stack.pop();
   if (next.right != null) {
    pullAll(next.right);
   }
   return next;
  }
  
  public TreeNode nextLeaf() {
   while(hasNext()) {
    TreeNode next = next();
    if (next.left == null && next.right == null) {
     return next;
    }
   }
   return null;
  }
  
  boolean hasNext() {
   return stack.isEmpty() == false;
  }
 }
 
 public static void main(String[] args) {
  TreeNode root1 = new TreeNode('A');
  root1.left = new TreeNode('B');
  root1.right = new TreeNode('C');
  root1.left.left = new TreeNode('D');
  root1.left.right = new TreeNode('E');
  TreeNode root2 = new TreeNode('A');
  root2.left = new TreeNode('D');
  root2.right = new TreeNode('B');
  char[] res = findFirstNonMatch(root1, root2);
  System.out.println(res);
 }
 
 static char[] findFirstNonMatch(TreeNode root1, TreeNode root2) {
  MyIterator iter1 = new MyIterator(root1);
  MyIterator iter2 = new MyIterator(root2);
  while(true) {
   TreeNode leaf1 = iter1.nextLeaf();
   TreeNode leaf2 = iter2.nextLeaf();
   if (leaf1 == null || leaf2 == null) break;
   if (leaf1.val != leaf2.val) {
    return new char[] {leaf1.val, leaf2.val};
   }
  }
  return new char[] {};
 }