Added solution

Author: avidLearnerInProgress

bst_to_greater_tree.cpp

@@ -0,0 +1,23 @@
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    
+    int sum = 0;
+    TreeNode* convertBST(TreeNode* root) {
+        if(root){
+            convertBST(root->right);
+            root->val += sum;
+            sum = root->val;
+            convertBST(root->left);
+        }
+        return root;
+    }
+};