adding general tree code

lectures/19_trees_II/general_tree_post_order.cpp

@@ -0,0 +1,79 @@
+#include <iostream>
+#include <vector>
+
+class Node {
+public:
+    int val;
+    std::vector<Node*> children;
+
+    Node() {}
+
+    Node(int _val) {
+        val = _val;
+    }
+
+    Node(int _val, std::vector<Node*> _children) {
+        val = _val;
+        children = _children;
+    }
+};
+
+// make a helper function, since the original one doesn't take the vector as a parameter.
+void postorder(Node* root, std::vector<int>& result){
+        // base case
+        if(root==NULL){
+            return;
+        }
+
+        // children first
+        int size = (root->children).size();
+        for(int i=0; i<size; ++i){
+            // call the same function to traverse children[i]
+            postorder(root->children[i], result);
+        }
+
+        // then parent
+        result.push_back(root->val);
+    }
+
+std::vector<int> postorder(Node* root) {
+    std::vector<int> result;
+    postorder(root, result);
+    return result;
+}
+
+int main() {
+    // create tree nodes
+    //     1
+    //  /  |  \
+    // 2   3   4
+    //    /  \
+    //   5    6
+    Node* node5 = new Node(5);
+    Node* node6 = new Node(6);
+    Node* node2 = new Node(2);
+    Node* node3 = new Node(3, {node5, node6});
+    Node* node4 = new Node(4);
+    Node* root = new Node(1, {node2, node3, node4});
+
+    // call preorder traversal
+    std::vector<int> result = postorder(root);
+
+    // print result
+    std::cout << "Post-order traversal: ";
+    for (int val : result) {
+        std::cout << val << " ";
+    }
+    std::cout << std::endl;
+
+    // free memory (optional but good practice)
+    delete node5;
+    delete node6;
+    delete node2;
+    delete node3;
+    delete node4;
+    delete root;
+
+    return 0;
+}
+