剑指 Offer 32 - III. 从上到下打印二叉树 III 发表于 2021-11-13 12345678910111213141516171819202122232425262728293031323334353637class Solution { public List<List<Integer>> levelOrder(TreeNode root) { if (root == null) { return Collections.emptyList(); } List<List<Integer>> resultList = new ArrayList<>(); Queue<TreeNode> queue = new LinkedList<>(); queue.add(root); while (!queue.isEmpty()) { LinkedList<Integer> deque = new LinkedList<>(); // 注意此处声明为 LinkedList 才能同时含有 Deque 与 List 接口 boolean leftToRight = (resultList.size() & 1) == 0; for (int i = queue.size(); i > 0; i--) { TreeNode node = queue.poll(); if (leftToRight) { deque.addLast(node.val); } else { deque.addFirst(node.val); } if (node.left != null) { queue.add(node.left); } if (node.right != null) { queue.add(node.right); } } resultList.add(deque); } return resultList; }} Reference剑指 Offer 32 - III. 从上到下打印二叉树 III