Finished live code

src/Traversal.java

@@ -1,5 +1,138 @@
+import java.util.*;
 public class Traversal {
   public static void main(String[] args) {
+    TreeNode<Integer> root = new TreeNode<Integer>(10, new TreeNode<Integer>(9, new TreeNode<Integer>(5, null, null), new TreeNode<Integer>(2, null, null)), new TreeNode<Integer>(15, new TreeNode<Integer>(-3, null, null), new TreeNode<Integer>(5, null, new TreeNode<Integer>(22, null, null))));
+
+    // preorder(root);
+    // System.out.println();
+    // postorder(root);
+    // System.out.println();
+    // inorder(root);
+    // System.out.println();
 
+    TreeNode<String> stringRoot = new TreeNode<String>("Hello", new TreeNode<String>("Hello", new TreeNode<String>("am", null, null), new TreeNode<String>("am", null, null)), new TreeNode<String>("I", new TreeNode<String>("am", null, null), new TreeNode<String>("so", null, new TreeNode<String>("good", null, null))));
+
+    TreeNode<Integer> megaRoot = new TreeNode<Integer>(1, null, null);
+
+    TreeNode<Integer> current = megaRoot;
+
+    for (int i = 2; i < 5000; i++) {
+      current.right = new TreeNode<Integer>(i, null, null);
+      current = current.right;
+    }
+
+    // preorder(megaRoot);
+
+    levelOrder(root);
+
+    // System.out.println("Preorder Recursive: ");
+    // preorder(root);
+    // System.out.println();
+    // System.out.println("Preorder Iterative");
+    // preOrderIter(megaRoot);
+    // System.out.println();
+
+    // System.out.println();
+
+    // preorder(stringRoot);
+    // System.out.println();
+    // postorder(stringRoot);
+    // System.out.println();
+    // inorder(stringRoot);
+    // System.out.println();
+
+    // printGreater(root, 10);
+    // System.out.println();
+
+    // System.out.println(countNodes(root));
+    // System.out.println(toMap(stringRoot));
+
+  }
+
+  public static <T> void levelOrder(TreeNode<T> node){
+    Queue<TreeNode<T>> queue = new LinkedList<>();
+
+    queue.add(node);
+
+    while(!queue.isEmpty()){
+      TreeNode<T> current = queue.poll();
+
+      if(current == null){
+        continue;
+      }
+
+      System.out.print(current.value + " ");
+      queue.add(current.left);
+      queue.add(current.right);
+    }
+  }
+
+  public static <T> void preOrderIter(TreeNode<T> node) {
+    Stack<TreeNode<T>> stack = new Stack<>();
+    stack.push(node); 
+
+    while(!stack.isEmpty()) {
+      TreeNode<T> current = stack.pop();
+      if (current == null) continue;
+      System.out.print(current.value + " ");
+      stack.push(current.right);
+      stack.push(current.left);
+    }
+  }
+
+  public static <T> Map<T, Integer> toMap(TreeNode<T> node) {
+    Map<T, Integer> counts = new HashMap<>();
+    toMap(node, counts);
+    return counts;
+  }
+
+  private static <T> void toMap(TreeNode<T> node, Map<T, Integer> counts) {
+    if (node == null) {
+      return;
+    }
+    counts.put(node.value, counts.getOrDefault(node.value, 0) + 1);
+    toMap(node.left, counts);
+    toMap(node.right, counts);
+  }
+
+  public static int countNodes(TreeNode<?> node) {
+    int count = 0;
+    if (node == null) {
+      return 0;
+    } else {
+      count++;
+      count += (countNodes(node.right) + countNodes(node.left)); 
+    }
+    return count;
+  }
+
+  public static void printGreater(TreeNode<Integer> node, int threshold) {
+    if (node == null) return;
+    if (node.value > threshold) {
+      System.out.print(node.value + " ");
+    }
+    printGreater(node.left, threshold);
+    printGreater(node.right, threshold);
+  }
+
+  public static <T> void preorder(TreeNode<T> node) {
+    if (node == null) return;
+    System.out.print(node.value + " ");
+    preorder(node.left);
+    preorder(node.right);
+  }
+
+  public static <T> void postorder(TreeNode<T> node) {
+    if (node == null) return;
+    postorder(node.left);
+    postorder(node.right);
+    System.out.print(node.value + " ");
+  }
+
+  public static <T> void inorder(TreeNode<T> node) {
+    if (node == null) return;
+    inorder(node.left);
+    System.out.print(node.value + " ");
+    inorder(node.right);
   }
 }

src/TreeNode.java

@@ -1,4 +1,17 @@
-public class TreeNode {
+public class TreeNode<T> {
+    // -- Instance fields --
 
-
+    // The value of the node
+    public T value;
+
+    // Left and right pointers
+    public TreeNode<T> left;
+    public TreeNode<T> right;
+
+    // -- Contructors --
+    public TreeNode(T value, TreeNode<T> left, TreeNode<T> right) {
+        this.value = value;
+        this.left = left;
+        this.right = right;
+    }
 }