Create TopViewOfBT.java

Binary Tree/TopViewOfBT.java

@@ -0,0 +1,96 @@
+import java.util.Scanner;
+import java.util.LinkedList;
+import java.util.Queue;
+import java.util.Stack;
+import java.util.ArrayList;
+import java.util.TreeMap;
+
+class Node{
+    int val;
+    Node left;
+    Node right;
+    Node(int val){
+        this.val = val;
+        this.left = this.right = null;
+    }
+}
+
+class TopViewOfBT{
+    static Node root;
+    static Queue<Node> queue = new LinkedList<>(); //queue is only responsible for tracking nodes whose children need processing.
+
+    static void insert(int[] nodes){
+
+        root = new Node(nodes[0]);
+        queue.add(root);
+        int i = 1;
+
+        while(!queue.isEmpty()){
+            Node currentNode = queue.poll();
+            if(i<nodes.length){
+                currentNode.left = new Node(nodes[i++]);
+                queue.add(currentNode.left);
+            }
+            if(i<nodes.length){
+                currentNode.right = new Node(nodes[i++]);
+                queue.add(currentNode.right);
+            }
+        }
+    }
+
+    static ArrayList<Integer> topView(Node root){ //needa incorporate depth tracking to ensure that shallower nodes are processed porperly and not overshadowed.
+        int hd = 0;
+        TreeMap<Integer, Integer> map = new TreeMap<Integer, Integer>(); //TreeMap over HashMap at it sorts the hd
+        dfs(root, hd, map);
+        ArrayList<Integer> list = new ArrayList<>();
+        for(int ele : map.keySet()){
+            System.out.println(map.get(ele));
+            list.add(map.get(ele));
+        }
+        return list;
+    }
+
+    static void dfs(Node root, int hd, TreeMap<Integer, Integer> map){
+        if(root == null){
+            return;
+        }
+        if(!map.containsKey(hd)){
+            map.put(hd, root.val);
+        }
+        dfs(root.left, hd-1, map);
+        //System.out.print(" " + root.val);
+        dfs(root.right, hd+1, map);
+    }
+
+    static void preorder(Node root){ // Root -> Left -> Right
+        if(root == null){
+            return;
+        }
+
+        System.out.print(" " + root.val);
+        preorder(root.left);
+        preorder(root.right);
+    }
+
+    public static void main(String[] args){
+        Scanner input = new Scanner(System.in);
+        System.out.println("Enter the number of nodes: ");
+        int numOfNodes = input.nextInt();
+        System.out.println("Enter the nodes: ");
+        int[] nodes = new int[numOfNodes];
+        for(int i = 0; i<numOfNodes; i++){
+            nodes[i] = input.nextInt(); //10 5 null 3 7 13 20
+        }
+
+        insert(nodes);
+        System.out.println("Pre-order:");
+        preorder(root);
+        System.out.println();
+        //System.out.println("DFS:");
+        //dfs(root);
+        System.out.println("Top view of a BT: ");
+        topView(root);
+
+        input.close();
+    }
+}