LC#226 invert a binary tree, iterative & recursive approach, O(N) time & space

Author: NirmalSilwal

Leetcode/easy/InvertBinaryTree226.java

@@ -1,5 +1,8 @@
 package easy;
 
+import java.util.LinkedList;
+import java.util.Queue;
+
 public class InvertBinaryTree226 {
 
 	private class TreeNode {
@@ -36,4 +39,46 @@ public TreeNode invertTree(TreeNode root) {
 
 		return root;
 	}
+
+	public TreeNode invertTree2(TreeNode root) {
+		if (root == null)
+			return null;
+
+		// swap left & right subtree
+		TreeNode tempnode = root.left;
+		root.left = root.right;
+		root.right = tempnode;
+
+		// recursively solve for children
+		invertTree(root.left);
+		invertTree(root.right);
+
+		return root;
+	}
+
+	public TreeNode invertTreeIterative(TreeNode root) {
+		if (root == null)
+			return null;
+
+		// bfs approach
+		Queue<TreeNode> queue = new LinkedList<TreeNode>();
+
+		queue.add(root);
+
+		while (!queue.isEmpty()) {
+			// remove from queue and swap children
+			TreeNode currentNode = queue.poll();
+			// swap
+			TreeNode temp = currentNode.left;
+			currentNode.left = currentNode.right;
+			currentNode.right = temp;
+
+			if (currentNode.left != null)
+				queue.add(currentNode.left);
+			if (currentNode.right != null)
+				queue.add(currentNode.right);
+		}
+
+		return root;
+	}
 }