Binary Search Tree

BST.java

public class TreeNode{
 public int data;
 public TreeNode left;
 public TreeNode right;
 public TreeNode(int d){
  this.data = d;
  this.left = null;
  this.right = null;
 }
}

public class BinarySearchTree{
 public root;
 public BinarySearchTree(){
  root = null;
 }
 
 public boolean addNode(int d){
  if (root == null){
   root = new TreeNode(d);
   return true;
  }
  else if (root.data == d){
   return false;
  }
  else{
   return addNodeHelper(root, d);
  }
 }
 
 private boolean addNodeHelper(TreeNode node, int d){
  if (d == node.data){
   return false;
  }
  else if (d < node.data){
   if (node.left == null){
    node.left = new TreeNode(d);
    return true;
   }
   else{
    return addNodeHelper(node.left, d);
   }
   else{
    if (node.right == null){
     node.right = new TreeNode(d);
     return true;
    }
    else{
     return addNodeHelper(node.right, d);
    }
   }
  }
 }
 
 public TreeNode find(int d){
  TreeNode curr = root;
  while (curr != null){
   if (curr.data == d){
    return curr;
   }
   else if (d < curr.data){
    curr = curr.left;
   }
   else{
    curr = curr.right;
   }
  }
  return null;
 }
 
 public TreeNode findLargest(TreeNode node){
  TreeNode curr = node;
  if (curr == null){
   return null;
  }
  while (curr.right != null){
   curr = curr.right;
  }
  return curr;
 }
 
 public TreeNode findSecondLargest(TreeNode node){
  TreeNode curr = node;
  while (curr != null){
   if (curr.right == null && curr.left != null){
    //largest is largest of left sub-tree
    return findLargest(curr.left);
   } 
   else if (curr.right != null && curr.right.right == null && curr.right.left == null){
    //curr is second largest, return it
    return curr;
   }
   curr = curr.right;
  }
  return null;
 }
 
}