adding Two Sum in BST solution

Author: Tanya401

Trees/TwoSumBST.cpp

@@ -0,0 +1,31 @@
+/**
+ * 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:
+    void inorder(TreeNode*root, vector<int>&ans){
+        if(root==NULL) return;
+       inorder(root->left,ans);
+        ans.push_back(root->val);
+        inorder(root->right,ans);
+    }
+    bool findTarget(TreeNode* root, int k) {
+        vector<int> ans;
+       inorder(root,ans);
+        int a=0, b=ans.size()-1;
+        while(a<b){
+            if(ans[a] + ans[b] == k) return true;
+            else if(ans[a] + ans[b] > k) b--;
+            else a++;
+        }
+        return false;
+    }
+};