live code

src/Traversal.java

@@ -1,5 +1,139 @@
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.Map;
+import java.util.Stack;
+import java.util.Queue;
+
 public class Traversal {
   public static void main(String[] args) {
+    TreeNode<Integer> root = new TreeNode<Integer>(10, null, null);
+    root.left = new TreeNode<Integer>(9, null, null);
+    root.left.left = new TreeNode<Integer>(5, null, null);
+    root.left.right = new TreeNode<Integer>(2, null, null);
+    root.right = new TreeNode<Integer>(15, null, null);
+    root.right.left = new TreeNode<Integer>(-3, null, null);
+    root.right.right = new TreeNode<Integer>(5, null, null);
+    root.right.right.right = new TreeNode<Integer>(22, null, null);
+
+
+    TreeNode<String> root2 = new TreeNode<String>("hello", null, null);
+    root2.left = new TreeNode<String>("how", null, null);
+    root2.left.left = new TreeNode<String>("are", null, null);
+    root2.left.right = new TreeNode<String>("you", null, null);
+    root2.right = new TreeNode<String>("i", null, null);
+    root2.right.left = new TreeNode<String>("am", null, null);
+    root2.right.right = new TreeNode<String>("so", null, null);
+    root2.right.right.right = new TreeNode<String>("good", null, null);
+/* 
+    System.out.println("======PRE ORDER======");
+    preorder(root);
+    System.out.println("======POST ORDER======");
+    postorder(root);
+    System.out.println("======IN ORDER======");
+    inorder(root);
+
+    printGreater(root, 7);
+*/
+    //System.out.println(countNodes(root));
+
+    TreeNode<Integer> megaRoot = new TreeNode<Integer>(1, null, null);
+
+    TreeNode<Integer> current = megaRoot;
+
+    for(int i = 2; i <= 50000; i++) {
+      current.right = new TreeNode<Integer>(i, null, null);
+      current = current.right;
+    }
+
+
+    levelOrder(root);
+    //preOrderIter(megaRoot);
+
+    /*System.out.println("Preorder recursive");
+    preorder(root);
+    System.out.println("Preorder iterative");
+    preOrderIter(root);*/
+  }
+
+  public static <T> void preOrderIter(TreeNode<T> node) {
+    Stack<TreeNode<T>> stack = new Stack<>();
+    stack.push(node);
+
+    while(!stack.empty()) {
+      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> 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.println(current.value);
+      queue.add(current.left);
+      queue.add(current.right);
+    }
+  }
+
+    //print tree rooted at given node in pre-order.
+  public static void preorder(TreeNode<?> node) {
+    if(node == null) return;
+    System.out.println(node.value);
+    preorder(node.left);
+    preorder(node.right);
+  }
+
+
+  public static int countNodes(TreeNode<?> node) {
+    if(node == null) return 0;
+    return 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 void postorder(TreeNode<?> node) {
+    if(node == null) return;
+    postorder(node.left);
+    postorder(node.right);
+    System.out.println(node.value);
+  }
+
+  public static void inorder(TreeNode<?> node) {
+    if(node == null) return;
+    inorder(node.left);
+    System.out.println(node.value);
+    inorder(node.right);
+  }
+
+  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);    
   }
-}
+}

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;
+    }
 }