常见错误

1. ArrayList, LinkedList

(1) 错：Queue<TreeNode> queue = new ArrayList<TreeNode>();

//error: incompatible types: ArrayList<TreeNode> cannot be converted to Queue<TreeNode>

 对：Queue<TreeNode> queue = new LinkedList<TreeNode>();

或： ArrayList<TreeNode> queue = new ArrayList<TreeNode>();

（2）错：Stack<TreeNode> stack = new LinkedList<TreeNode>();

//error: incompatible types: LinkedList<TreeNode> cannot be converted to Stack<TreeNode>

对：Stack<TreeNode> stack = new Stack<TreeNode>();

或：LinkedList<TreeNode> stack = new LinkedList<TreeNode>();