Create 623. Add One Row to Tree (#458)

Author: Chayandas07

623. Add One Row to Tree

@@ -0,0 +1,43 @@
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    TreeNode* addOneRow(TreeNode* root, int val, int depth) {
+        if (depth == 1) {
+            TreeNode* newRoot = new TreeNode(val);
+            newRoot->left = root;
+            return newRoot;
+        }
+        
+        TreeNode *result = addRow(root, val, depth);
+        return result;
+    }
+    
+    TreeNode* addRow(TreeNode *currentNode, int val, int depth) {
+        if (currentNode == nullptr)
+            return currentNode;
+        
+        if (depth == 2) {
+            TreeNode *newLeftNode = new TreeNode(val);
+            TreeNode *newRightNode = new TreeNode(val);
+            newLeftNode->left = currentNode->left;
+            newRightNode->right = currentNode->right;
+            currentNode->left = newLeftNode;
+            currentNode->right = newRightNode;
+            return currentNode;
+        }
+        
+        currentNode->left = addRow(currentNode->left, val, depth - 1);
+        currentNode->right = addRow(currentNode->right, val, depth - 1);
+        return currentNode;
+    }
+};