Added Binary_Tree_Postorder_Traversal.cpp

Binary search tree/Binary_Tree_Postorder_Traversal.cpp

@@ -0,0 +1,26 @@
+Approach #1: Recursive Method
+
+The recursive Approach is the straight forward and classical approach.
+
+If the current node is not empty :
+1. Traverse the left subtree
+2. Traverse the right subtree
+3.  Print the node
+
+class Solution {
+public:
+    vector<int> postorderTraversal(TreeNode* root) {
+        vector<int> nodes;
+        postorder(root, nodes);
+        return nodes;
+    }
+private:
+    void postorder(TreeNode* root, vector<int>& nodes) {
+        if (!root) {
+            return;
+        }
+        postorder(root -> left, nodes);
+        postorder(root -> right, nodes);
+        nodes.push_back(root -> val);
+    }
+};