tree questions leetcode

Author: kumar91gopi

README.md

@@ -193,11 +193,14 @@ solution of many challenges of [HackerRank](https://www.hackerrank.com) and [Cod
 
 #### Binary Trees
 1. [Invert Binary Tree](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/invert_binary_tree.rb)
+2. [Height of Binary Tree](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/max_depth_of_binary_tree.rb)
+
 
 <a name="bst"/>
 
 #### Binary Search Trees
 1. [Lowest Common Ancestor of BST](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/lowest_common_ancestor.rb)
+2. [Sorted Array to BST](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/sorted_array_to_bst.rb)
 
 <a name="dp"/>
 
@@ -259,7 +262,8 @@ solution of many challenges of [HackerRank](https://www.hackerrank.com) and [Cod
 24. [Climbing Stairs](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/climbing_stairs.rb)
 25. [Lowest Common Ancestor of BST](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/lowest_common_ancestor.rb)
 26. [Add Binary](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/add_binary.rb)
-
+27. [Max Depth of Binary Tree](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/max_depth_of_binary_tree.rb)
+28. [Sorted Array to BST](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/sorted_array_to_bst.rb)
 
 <a name="striver"/>
 

leetcode/grind75/add_binary.rb

@@ -13,7 +13,7 @@ def add_binary(a, b)
         char_b = j>=0 ? b[j] : '0'
         if char_a =='0' and char_b=='0'
             char,carry = carry>0 ? [1,0] : [0,0] 
-            result="#{char}#{result}"
+            result="#{char}#{result}" #instead of adding har in front you can append and reverse result in the end
         elsif (char_a=='0' and char_b=='1') or (char_a=='1' and char_b=='0')
             char,carry = carry>0 ? [0,1] : [1,0] 
             result="#{char}#{result}"

leetcode/grind75/max_depth_of_binary_tree.rb

@@ -0,0 +1,13 @@
+=begin
+Given the root of a binary tree, return its maximum depth.
+A binary tree's maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.
+=end
+
+# Solution 1 (Recursion)
+def max_depth(root)
+    return 0 if root.nil?
+    return 1+[max_depth(root.left),max_depth(root.right)].max
+end
+
+# Solution 2 (BFS)
+#TODO

leetcode/grind75/sorted_array_to_bst.rb

@@ -0,0 +1,20 @@
+=begin
+Given an integer array nums where the elements are sorted in ascending order, convert it to a 
+height-balanced binary search tree.
+=end
+
+#Solution
+def sorted_array_to_bst(nums)
+    l = 0
+    r = nums.length-1
+    create_bst(nums,l,r)
+end
+
+def create_bst(nums,l,r)
+    return nil if l>r
+    mid = (l+r)>>1
+    root = TreeNode.new(nums[mid])
+    root.left = create_bst(nums,l,mid-1)
+    root.right = create_bst(nums,mid+1,r)
+    root
+end