Tree Implement live code

src/Traversal.java

@@ -1,5 +1,188 @@
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.Queue;
+import java.util.List;
+import java.util.Map;
+import java.util.Stack;
+
 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> stringRoot = new TreeNode<String>("hello", null, null);
+    stringRoot.left = new TreeNode<String>("how", null, null);
+    stringRoot.left.left = new TreeNode<String>("are", null, null);
+    stringRoot.left.right = new TreeNode<String>("hello", null, null);
+
+    stringRoot.right = new TreeNode<String>("I", null, null);
+    stringRoot.right.left = new TreeNode<String>("am", null, null);
+    stringRoot.right.right = new TreeNode<String>("am", null, null);
+    stringRoot.right.right.right = new TreeNode<String>("good", null, null);
+
+    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);
+
+    TreeNode<Integer> newRoot = new TreeNode<Integer>(3, new TreeNode<Integer>(9, null, new TreeNode<Integer>(4, null, null)), null);
+    //newRoot.left = new TreeNode<Integer>(9, null, null);
+    //newRoot.left.right = new TreeNode<Integer>(4, null, null);
+    newRoot.right = new TreeNode<Integer>(4, null, null);
+    newRoot.right.left = new TreeNode<Integer>(9, null, null);
+    newRoot.right.right = new TreeNode<Integer>(6, null, null);
+    newRoot.right.right.left = new TreeNode<Integer>(4, null, null);
+
+    // { "hello": 1, "how": 2, "you": 1 }
+    List<String> wordList = List.of("hello", "how", "you", "how");
+    //System.out.println(listToMap(wordList));
+
+    //preorder(root);
+    //postorder(root);
+    //inorder(stringRoot);
+
+    //printGreater(root, 4);
+    //System.out.println(countNodes(root));
+
+    //System.out.println(toMap(stringRoot));
+  }
+
+  // Print a tree rooted at the given node in pre-order
+  public static void preorder(TreeNode<?> node) {
+    if (node == null) return; // if null, return
+    System.out.println(node.value); // print value 
+    preorder(node.left); // traverse left
+    preorder(node.right); // traverse right 
+  }
+
+  // depth first search 
+  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);      
+    }
+  }
+
+  // breath first search (level order)
+  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);
+    }
+  }
+
+  // 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 Map<String, Integer> listToMap(List<String> list){
+
+//     for word in list:
+//        if our word is a key in the map:
+// 	        newValue = map.get(word) + 1
+// 	        map.put(word, newValue)
+//        else:
+// 	        map.put(word, 1)
+
+    // "hello", "how", "you", "how"
+
+    Map<String, Integer> map = new HashMap<>(); // {"hello": 1, "how": 1, "you": 1}
+
+    int count = 0;
+
+    for (int i = 0; i < list.size(); i++) {
+      String word = list.get(i); // how 
+
+      if (map.containsKey(word)){
+        count = map.get(word) + 1; // value of count = 2
+        map.put(word, count);
+      } else {
+        map.put(word, 1);
+      }
+    }
+    return map;
+  }
+
+
+  public static int countNodes(TreeNode<?> node) {
+    if (node == null) return 0;
+    return countNodes(node.left) + countNodes(node.right) + 1;
+
+    //return node == null ? 0 : countNodes(node.left) + countNodes(node.right) + 1;
+
+    // int leftCount = countNodes(node.left);
+    // int rightCount = countNodes(node.right);
+    // int overallCount = leftCount + rightCount + 1;
+    // return overallCount;
+  }
+
+  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);
+  }
+
+  // Print a tree rooted at the given node in post-order
+  public static <T> void postorder(TreeNode<T> node) {
+    if (node == null) return;
+    postorder(node.left);
+    postorder(node.right);
+    System.out.println(node.value);
+  }
 
+  // Print a tree rooted at the given node in in-order
+  public static <E> void inorder(TreeNode<E> node) {
+    if (node == null) return;
+    inorder(node.left);
+    System.out.println(node.value);
+    inorder(node.right);
   }
-}
+}

src/TreeNode.java

@@ -1,4 +1,11 @@
-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;
+    }
 }