Compelted live code

src/TreeNode.java

@@ -1,4 +1,12 @@
-public class TreeNode {
+public class TreeNode<T> {
+    public T value;
+    public TreeNode<T> left;
+    public TreeNode<T> right;
+
+    public TreeNode(T value, TreeNode<T> left, TreeNode<T> right){
+        this.value = value;
+        this.left = left;
+        this.right = right;
+    }
 
-
 }

src/toMap.java

@@ -0,0 +1,136 @@
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Stack;
+
+public class toMap {
+  public static void main(String[] args) {
+    TreeNode<Integer> root = new TreeNode<>(2, null, null);
+    root.left = new TreeNode<>(1, null, null);
+    root.left.left = new TreeNode<>(7, null, null);
+    root.left.right = new TreeNode<>(4, null, null);
+
+    root.right = new TreeNode<>(3, null, null);
+    root.right.left = new TreeNode<>(5, null, null);
+    root.right.right = new TreeNode<>(6, null, null);
+    root.right.right = new TreeNode<>(9, null, null);
+    root.right.right.right  = new TreeNode<>(8, null, null);
+
+    TreeNode<String> stringRoot = new TreeNode<>("hello",null,null);
+    stringRoot.left = new TreeNode<>("hello", null, null);
+    stringRoot.left.left = new TreeNode<>("hello", null, null);
+    stringRoot.left.right = new TreeNode<>("hello", null, null);
+
+    stringRoot.right = new TreeNode<>("am", null, null);
+    stringRoot.right.left = new TreeNode<>("am", null, null);
+    stringRoot.right.right = new TreeNode<>("am", null, null);
+    stringRoot.right.right.right = new TreeNode<>("good", null, null);
+
+    TreeNode<Integer> megaRoot = new TreeNode<Integer>(1, null, null);
+
+    TreeNode<Integer> current = megaRoot;
+
+    for(int i = 2; i <= Integer.MAX_VALUE; i++){
+      current.right = new TreeNode<Integer>(i, null, null);
+      current = current.right;
+    }
+    // System.out.println("Preorder recursive");
+    // preorder(root);
+    // System.out.println("Preorder iterative");
+    //  preOrderIter(root);
+    preOrderIter(megaRoot);
+
+    // 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 void preorder(TreeNode<Integer> node){
+    if(node == null) return;
+    System.out.println(node.value);
+    preorder(node.left);
+    preorder(node.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.println(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;
+    }
+
+    // fill up those counts
+    counts.put(node.value, counts.getOrDefault(node.value, 0) + 1);
+
+    toMap(node.left, counts);
+    toMap(node.right, counts);    
+  }
+
+  public static int countNodes(TreeNode<?> node){
+   return node == null ? 0 : 1 + countNodes(node.left) + countNodes(node.right);
+  }
+
+  public static void printGreater(TreeNode<Integer> node, int threshold){
+    if(node == null) return;
+    if(node.value > threshold){
+        System.out.println(node.value);
+
+    }
+    printGreater(node.left,threshold);
+    printGreater(node.right,threshold);
+  }
+
+  public static <T> void inorder(TreeNode<T> node){
+    if(node == null) return;
+    inorder(node.left);
+    System.out.print(node.value + " ");
+    inorder(node.right);
+  }
+
+  public static <E> void postorder(TreeNode<E> node){
+    if(node == null) return;
+    postorder(node.left);
+    postorder(node.right);
+    System.out.print(node.value + " ");
+  }
+
+
+}