leetcode102&107二叉树层次遍历I&II

public List<List<Integer>> levelOrder(TreeNode root) {
    List<List<Integer>> res = new ArrayList();
    if(root == null) return res;
    Deque<TreeNode> q = new LinkedList();
    q.offer(root);
    while(!q.isEmpty()) {
        int size = q.size();
        List<Integer> list = new ArrayList();
        while(size > 0) {
            TreeNode treeNode = q.poll();
            list.add(treeNode.val);
            if(treeNode.left != null) q.offer(treeNode.left);
            if(treeNode.right != null) q.offer(treeNode.right);
            size--;
        }
        res.add(list);
    }
    return res;
}

public List<List<Integer>> levelOrderBottom(TreeNode root) {
    List<List<Integer>> res = new ArrayList();
    if(root == null) return res;
    Deque<TreeNode> q = new LinkedList();
    q.offer(root);
    while(!q.isEmpty()) {
        int size = q.size();
        List<Integer> list = new ArrayList();
        for(int i = 0; i < size; i++) {
            TreeNode node = q.poll();
            list.add(node.val);
            if(node.left != null) q.offer(node.left);
            if(node.right != null) q.offer(node.right);
        }
        res.add(list);
    }
    Collections.reverse(res);
    return res;
}