Tree-Implement

src/Traversal.java

@@ -1,5 +1,174 @@
+import java.util.HashMap;
+import java.util.LinkedHashSet;
+import java.util.Map;
+import java.util.Stack;
+import java.util.Queue;
+import java.util.LinkedList;
+
+
+
 public class Traversal {
   public static void main(String[] args) {
+    TreeNode<Integer> root = new TreeNode<Integer>(10, null, null);
+    // TreeNode 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>("you", null, null);
+    stringRoot.right.left = new TreeNode<String>("i", null, null);
+    stringRoot.right.right = new TreeNode<String>("miss",  null, null);
+    stringRoot.right.right.right = new TreeNode<String>("you",  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);
 
+    // // preOrder(root); // root in the beginning
+    // postOrder(root); // root in the end
+    // inOrder(root); // root in the middle
+    // printGreater(root, 100);
+    // System.out.println(countNodes(root));
+    // Map<String, Integer> counts = new HashMap<>();
+    // System.out.println(toMap(stringRoot));
+
+  } 
+    // print a tree routed at the given node in pre order
+    public static void preOrder(TreeNode<?> node) {
+      if(node == null) {// if full return
+        return;
+      }
+      System.out.println(node.value);  // print value
+      preOrder(node.left); // traverse left 
+      preOrder(node.right); // traverse  right
+
+    }
+
+  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;
+      }
+
+      // if (current != null) {
+      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;
+      }
+
+      // if (current != null) {
+      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 the 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) {
+    // if node is null : return 0;
+    if (node == null) return 0;
+    return 1 + countNodes(node.left) + countNodes(node.right);
+
+    // or
+    // return node == null? 0 : 1 + countNodes(node.left) + countNodes(node.right);
+
+
+    // // leftCount = count nodes in left subtree
+    // int leftCount = countNodes(node.left);
+    // // rightCount = count nodes in right subtree
+    // int rightCount = countNodes(node.right);
+    // // overallCount = leftcount + rightcount + 1 --> 1 is th eparent
+    // int overallCount = leftCount + rightCount + 1;
+    // // return  overallCount
+    // 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 after recursion
+        public static <T> void postOrder(TreeNode<T> node) {
+          if (node == null) return;
+          postOrder(node.left);
+          postOrder(node.right);
+          System.out.println(node.value);
+        }
+
+        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 +1,14 @@
-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;
+
+    }
 
 
 }