Add Vertical Order Traversal (#2585)

DataStructures/Trees/VerticalOrderTraversal.java

@@ -0,0 +1,106 @@
+package DataStructures.Trees;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.Map;
+import java.util.Queue;
+
+/* The following class implements a vertical order traversal
+in a tree from top to bottom and left to right, so for a tree :
+           1
+          / \
+         2   3
+        / \   \
+       4   5   6
+        \     / \
+         7   8   10
+          \
+           9
+ the sequence will be :
+ 4 2 7 1 5 9 3 8 6 10
+ */
+public class VerticalOrderTraversal{
+
+	
+	public static void main(String[] args) {
+		BinaryTree tree = new BinaryTree();
+		tree.put(5);
+		tree.put(6);
+		tree.put(3);
+		tree.put(1);
+		tree.put(4);
+		BinaryTree.Node root = tree.getRoot();
+		ArrayList<Integer> ans = verticalTraversal(root);
+		for(int i : ans) {
+			System.out.print(i+" ");
+		}
+	}
+	 
+	/*Function that receives a root Node and prints the tree 
+	in Vertical Order.*/
+	private static ArrayList<Integer> verticalTraversal(BinaryTree.Node root) {
+		/*Queue to store the Nodes.*/
+		Queue<BinaryTree.Node> queue= new LinkedList<>(); 
+		
+		/*Queue to store the index of particular vertical 
+		 column of a tree , with root at 0, Nodes on left 
+		 with negative index and Nodes on right with positive
+		 index. */
+		Queue<Integer> index = new LinkedList<>();
+		
+		/*Map of Integer and ArrayList to store all the 
+		 elements in a particular index in a single arrayList
+		 that will have a key equal to the index itself. */
+		Map<Integer,ArrayList<Integer>> map = new HashMap<>();
+		
+		/* min and max stores leftmost and right most index to
+		 later print the tree in vertical fashion.*/
+		int max =0, min =0;
+		queue.offer(root);
+		index.offer(0);
+		
+		while(!queue.isEmpty()) {
+			
+			if(queue.peek().left!=null) {
+				/*Adding the left Node if it is not null
+				and its index by subtracting 1 from it's 
+				parent's index*/
+				queue.offer(queue.peek().left);
+				index.offer(index.peek()-1);
+			}
+			if(queue.peek().right!=null) {
+				/*Adding the right Node if it is not null
+				and its index by adding 1 from it's 
+				parent's index*/
+				queue.offer(queue.peek().right);
+				index.offer(index.peek()+1);
+			}
+			/*If the map does not contains the index a new
+			 ArrayList is created with the index as key.*/
+			if(!map.containsKey(index.peek())) {
+				ArrayList<Integer> a = new ArrayList<>();			
+			    map.put(index.peek(), a);
+		    }
+			/*For a index, corresponding Node data is added
+			 to the respective ArrayList present at that
+			 index. */
+			map.get(index.peek()).add(queue.peek().data);
+			max = (int)Math.max(max,index.peek());
+			min = (int)Math.min(min,index.peek());
+			/*The Node and its index are removed 
+			 from their respective queues.*/
+			index.poll();queue.poll();
+		}
+		/*Finally map data is printed here which has keys
+		from min to max. Each ArrayList represents a 
+		vertical column that is added in ans ArrayList.*/
+		ArrayList<Integer> ans= new ArrayList<>();
+		for(int i =min ; i<= max ; i++) {
+			for(int j = 0 ; j<map.get(i).size(); j++) {
+				ans.add(map.get(i).get(j));
+			}
+		}
+		return ans;
+	}
+}