[leetcode] Binary Tree Level Order Traversal II

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public class Solution { List<List<Integer>> result = new ArrayList<List<Integer>>(); public List<List<Integer>> levelOrderBottom(TreeNode root) { dfsLevel(root, 0); Collections.reverse(result); return result; } private void dfsLevel(TreeNode root, int level){ if (root == null) return; if (result.size() < level+1) result.add(new ArrayList<Integer>()); result.get(level).add(root.val); dfsLevel(root.left, level+1); dfsLevel(root.right, level+1); } }