squashing commit

Tree_Preorder_Traversal/Tree_Preorder_Traversal.dart

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+import 'dart:io';
+
+// Class to define the node of a binary tree.
+class Node {
+
+    int value;
+    Node left;
+    Node right;
+
+    Node(int value) {
+
+        this.value = value;
+        this.left = null;
+        this.right = null;
+
+    }
+
+}
+
+// Class to define a binary tree.
+class Tree {
+
+    // The tree's root.
+    Node root;
+
+    // Constructor
+    Tree(Node root) {
+        this.root = root;
+    }
+
+    // Insert method to build the tree using recursion.
+    Node insert(Node root, int val) {
+
+        if (root != null){
+
+            // Inserting in the left side if value is less than root.
+            if (val < root.value) {
+                root.left = insert(root.left, val);
+            }
+            else {
+                // Inserting in the right side if value is greater than root.
+                if (val > root.value) {
+                    root.right = insert(root.right, val);
+                }
+                // Informing user that the value is already present.
+                else{
+                    print("Value is already present in the tree.");
+                }
+            }
+        }
+        else{
+            // Insertion 
+            root = Node(val);
+        }
+
+        return root;
+
+    }
+
+    // Utility method used to print the preorder traversal using recursion.
+    void preorder_utility(Node node) {
+
+        if (node != null) {
+            print(node.value);
+
+            // Recursion
+            preorder_utility(node.left);
+            preorder_utility(node.right);
+        }
+
+    }
+
+    // Method to print the preorder traversal of the binary tree.
+    void tree_preorder_traversal(){
+
+        print("The preorder traversal of the tree in the given input is follows:");
+        preorder_utility(this.root);
+
+    }
+
+}
+
+// Driver method of the program
+void main(){
+
+    // Reading user input
+    print("Enter root of the tree:");
+    var input = stdin.readLineSync();
+    int root_val = int.parse(input);
+
+    // Root node
+    Node root_node = Node(root_val);
+
+    // Binary Tree
+    Tree tree = Tree(root_node);
+
+    String choice = "y";
+
+    while (choice == "y") {
+
+        print("Enter number to insert:");
+        var input3 = stdin.readLineSync();
+        int insert_val = int.parse(input3);
+        tree.insert(root_node, insert_val);
+
+        print("Do you want to insert another number into the tree? (y/n)");
+        var input2 = stdin.readLineSync();
+        choice = input2;
+
+    }
+
+    /* Sample Input tree
+             8
+           /   \
+          3    12
+         / \   / \
+        2   6  9  15
+           / \
+          5   7
+    */
+
+    // Calling method to print preorder traversal of the tree.
+    tree.tree_preorder_traversal();
+
+    /* Sample Output
+      The preorder traversal of the tree in the given input is follows:
+      8
+      3
+      2
+      6
+      5
+      7
+      12
+      9
+      15
+    */
+
+}
+