剑指offer-面试题32 - II. 从上到下打印二叉树 II

[GuoLizhi]

BFS

时间复杂度O(n) 空间复杂度O(n)

class Solution {
    public List<List<Integer>> levelOrder(TreeNode root) {
        List<List<Integer>> result = new ArrayList<>();
        if (root == null) return result;
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            int sz = queue.size();
            List<Integer> line = new ArrayList<>();
            for (int i = 0; i < sz; i++) {
                TreeNode cur = queue.poll();
                line.add(cur.val);

                if (cur.left != null)
                    queue.offer(cur.left);
                if (cur.right != null)
                    queue.offer(cur.right);
            }
            result.add(line);
        }
        return result;
    }
}