Leetcode 107 : 二叉树的层次遍历2

https://leetcode-cn.com/problems/binary-tree-inorder-traversal/

考察点： 二叉树的层次遍历， 集合类的灵活应用 Collections 以及 list.add(0,)方法的灵活使用

    import BasicDataStruct.TreeNode; 

    import java.util.*;

    public class LeetCode107FLoorTraversal {

        public static List<List<Integer>> inorderTraversal(TreeNode root) {

            List<List<Integer>> list = new ArrayList<>();
            Queue<TreeNode> queue = new LinkedList<>();
            queue.offer(root);
            while (!queue.isEmpty()) {
                int size = queue.size();
                List<Integer> subList = new ArrayList<>();
                for (int i = 0; i < size; i++) {
                    TreeNode node = queue.poll();
                    subList.add(node.getVal());
                    if (node.left != null) {
                        queue.add(node.left);
                    }
                    if (node.right != null) {
                        queue.add(node.right);
                    }
                }
                // 也可以list.add(0,subList);
                list.add(subList);
            }
            Collections.reverse(list);
            
            return list;
        }


        public static void main(String[] args) {
            TreeNode root = new TreeNode(1);
            root.left = new TreeNode(2);
            root.right = new TreeNode(3);
            root.left.left = new TreeNode(4);
            root.left.right = new TreeNode(5);
            root.right.left = new TreeNode(6);
            root.right.right = new TreeNode(7);
            System.out.println(inorderTraversal(root).toString());
        }

    }