Add 129_Sum_Root_to_Leaf_Numbers.java

Author: Sean Prashad

Tree Depth First Search/129_Sum_Root_to_Leaf_Numbers.java

@@ -0,0 +1,24 @@
+class Solution {
+    public int sumNumbers(TreeNode root) {
+        if (root == null) {
+            return 0;
+        }
+        return dfs(root, 0);
+    }
+
+    private int dfs(TreeNode root, int levelBase) {
+        if (root == null) {
+            return 0;
+        }
+
+        if (root.left == null && root.right == null) {
+            return levelBase + root.val;
+        }
+
+        int nextLevelBase = 10 * (levelBase + root.val);
+        int left = dfs(root.left, nextLevelBase);
+        int right = dfs(root.right, nextLevelBase);
+
+        return left + right;
+    }
+}