AC Java DFS solution

  • 0
     public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
            List<List<Integer>> list = new ArrayList<>();
            helper(root, 0, list);
            return list;
        public void helper(TreeNode root, int level, List<List<Integer>> list){
            if(root == null) return;
            if(list.size() == level)
                list.add(new LinkedList<>());
            if(level % 2 == 0) 
                list.get(level).add(0, root.val);
            helper(root.left, level+1, list);
            helper(root.right, level+1, list);

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