102_Binary_Tree_Level_Order_Traversal.java

classSolution {
publicList<List<Integer>> levelOrder(TreeNoderoot) {
List<List<Integer>> res = newArrayList<>();
dfs(root, res, 0);
returnres;
 }

privatevoiddfs(TreeNoderoot, List<List<Integer>> res, intlevel) {
if (root == null) {
return;
 }

if (level >= res.size()) {
res.add(newArrayList<>());
 }

res.get(level).add(root.val);
dfs(root.left, res, level + 1);
dfs(root.right, res, level + 1);
 }
}