public void inOrderSearch(TreeNode root){
  if(root==null) return void;
  Stack<TreeNode> stack = new Stack<>();
  TreeNode p = root;
  while(!stack.isEmpty() || p!=null){
    if(p!=null){
      stack.push(p);
      p = p.left;
    }else{
      p = stack.top();
      stack.pop();
      System.out.println(p.value);
      p=p.right;
    }
  }
}