boundary traversal of BT

Author: Arjiit

Trees/boundaryBinaryTree.java

@@ -0,0 +1,41 @@
+class Solution {	
+	class TreeNode {
+		int data;
+		Node left, right;
+		public TreeNode(int data) {
+			this.data = data;
+			left = right = null;
+		}
+	}
+
+	public List<Integer> boundaryTraversal(TreeNode root) {
+		List<Integer> res = new ArrayList<>();
+		getBoundary(root, res, -1);
+		getBoundary(root, res,  0);
+		getBoundary(root, res,  1);
+
+		return res;			
+	}
+
+	public void getBoundary(TreeNode root, List<Integer> res, int dir) {
+		if (root == null) return;
+
+		if (dir == -1) {
+			if (root.left != null) {
+				res.add(root.val);
+				getBoundary(root.left, res, dir);
+			} 
+		} else if (dir == 0) {
+			getBoundary(root.left, res, dir);
+			if (root.left == null && root.right == null) {
+				res.add(root.val);
+			}
+			getBoundary(root.right, res, dir);
+		} else if (dir == 1) {
+			if (root.right != null) {
+				res.add(root.val);
+				getBoundary(root.right, res, dir);
+			}
+		}
+	}
+}