题目
题链：剑指 Offer 32 - II. 从上到下打印二叉树 II
题解
广度优先遍历、加一个循环分层。
大佬详细题解：剑指 Offer 32 - II. 从上到下打印二叉树 II
/*** Definition for a binary tree node.* public class TreeNode {*int val;*TreeNode left;*TreeNode right;*TreeNode(int x) { val = x; }* }*/class Solution {public List<List<Integer>> levelOrder(TreeNode root) {if (root == null){return new ArrayList<>();}Queue<TreeNode> queue = new LinkedList<>();queue.offer(root);List<List<Integer>> res = new ArrayList<>();while (!queue.isEmpty()){List<Integer> ans = new ArrayList<>();for (int i = queue.size(); i >0; i--) {TreeNode node = queue.poll();if (node.left != null){queue.offer(node.left);}if (node.right != null){queue.offer(node.right);}ans.add(node.val);}res.add(ans);}return res;}}
