leetcode level order traversal

Author: kumar91gopi

README.md

@@ -209,7 +209,7 @@ solution of many challenges of [Leetcode](https://leetcode.com/), [Exercism](htt
 8. [Balanced Binary tree](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/balanced_binary_tree.rb)
 9. [Symmetric Tree](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/symmetric_tree.rb)
 10. [Subtree of Another Tree](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/subtree_of_another_tree.rb)
-
+11. [Binary Tree Level order Traversal](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/binary_tree_level_order_traversal.rb)
 
 <a name="bst"/>
 
@@ -308,6 +308,7 @@ solution of many challenges of [Leetcode](https://leetcode.com/), [Exercism](htt
 
 ## [LeetCode](https://leetcode.com/problems)
 1. [Insert Delete GetRandom in O(1)](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/insert_delete_get_random_o1.rb)
+2. [Binary Tree Level order Traversal](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/binary_tree_level_order_traversal.rb)
 
 <a name="grind-75"/>
 

leetcode/binary_tree_level_order_traversal.rb

@@ -0,0 +1,37 @@
+=begin
+Problem: https://leetcode.com/problems/binary-tree-level-order-traversal/description/
+Given the root of a binary tree, return the level order traversal of its nodes' values. (i.e., from left to right, level by level).
+=end
+
+#Solution (Using BFS/Queue)
+
+# Definition for a binary tree node.
+# class TreeNode
+#     attr_accessor :val, :left, :right
+#     def initialize(val = 0, left = nil, right = nil)
+#         @val = val
+#         @left = left
+#         @right = right
+#     end
+# end
+# @param {TreeNode} root
+# @return {Integer[][]}
+def level_order(root)
+    val_list = []
+    return [] if root.nil?
+    queue = [root] # Queue.new can be used instead of List for efficiency of insertion
+
+    until queue.empty?
+        level = []
+        size = queue.length
+
+        size.times do
+            node =  queue.pop()
+            level.append(node.val)
+            queue.unshift(node.left) if node.left
+            queue.unshift(node.right) if node.right
+        end
+        val_list.append(level)
+    end
+    val_list
+end