Binary Tree Level Order Traversal

Author: TonyKim9401

binary-tree-level-order-traversal/TonyKim9401.java

@@ -0,0 +1,26 @@
+// TC: O(n)
+// need to visit all nodes
+// SC: O(n)
+// normally O(log n) required however, O(n) in the worst case
+class Solution {
+    private List<List<Integer>> output = new ArrayList<>();
+    public List<List<Integer>> levelOrder(TreeNode root) {
+        dsf(0, root);
+        return output;
+    }
+
+    private void dsf(int level, TreeNode node) {
+        if (node == null) return;
+
+        if (output.size() == level) {
+            List<Integer> inside = new ArrayList<>();
+            inside.add(node.val);
+            output.add(inside);
+        } else {
+            output.get(level).add(node.val);
+        }
+        level += 1;
+        dsf(level, node.left);
+        dsf(level, node.right);
+    }
+}