#250 Binary Tree Level Order Traversal

Author: forest000014

binary-tree-level-order-traversal/forest000014.java

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+/*
+# Time Complexity: O(n)
+# Space Complexity: O(n)
+  - 재귀 호출 함수의 파라미터 root, depth, ans
+*/
+
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+class Solution {
+    public List<List<Integer>> levelOrder(TreeNode root) {
+        List<List<Integer>> ans = new ArrayList<>();
+
+        dfs(root, 0, ans);
+
+        return ans;
+    }
+
+    private void dfs(TreeNode root, int depth, List<List<Integer>> ans) {
+        if (root == null) return;
+
+        if (ans.size() == depth) {
+            ans.add(new ArrayList<>());
+        }
+        ans.get(depth).add(root.val);
+
+        dfs(root.left, depth + 1, ans);
+        dfs(root.right, depth + 1, ans);
+    }
+}