bin_tree_scan.java

public class Node {
  int val;
  Node left;
  Node right;
}

public void preOrderScan(Node root) {
  if (root == null) return;
  
  Stack s = new Stack();
  s.push(root);
  while (!s.isEmpty()) {
    Node cur = s.pop();
    print(cur);
    
    if (cur.right != null) s.push(cur.right);
    if (cur.left != null) s.push(cur.left);
  }
}

public void inOrderScan(Node root) {
  if (root == null) return;
  
  Stack s = new Stack();
  Node cur = root;
  While (!s.isEmpty() || cur != null) {
    if (cur != null) {
      s.push(cur);
      cur = cur.left;
    } else {
      cur = s.pop();
      print(cur);
      
      cur = cur.right;
    }
  }
}