more leetcode questions

Author: kumar91gopi

Diff for: README.md

@@ -175,6 +175,7 @@ solution of many challenges of [HackerRank](https://www.hackerrank.com) and [Cod
 5. [Find missing number in array(Approach 2)](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/arrays/FindMissingNumber.rb)
 6. [Find two repeating elements in given array(Approach 4)](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/arrays/FindTwoRepeatingElem.rb)
 7. [Add Binary](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/add_binary.rb)
+8. [Counting Bits](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/counting_bits.rb)
 
 <a name="maths"/>
 
@@ -194,7 +195,7 @@ 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)
-
+3. [Same Tree](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/same_tree.rb)
 
 <a name="bst"/>
 
@@ -264,6 +265,9 @@ solution of many challenges of [HackerRank](https://www.hackerrank.com) and [Cod
 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)
+29. [Maximum Subarray Sum](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/maximum_subarray_sum.rb)
+30. [Same Tree](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/same_tree.rb)
+31. [Counting Bits](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/grind75/counting_bits.rb)
 
 <a name="striver"/>
 

Diff for: leetcode/grind75/counting_bits.rb

@@ -0,0 +1,45 @@
+=begin
+Given an integer n, return an array ans of length n + 1 such that for each i (0 <= i <= n),
+ans[i] is the number of 1's in the binary representation of i.
+=end
+
+#Solution 1 (O(n log n))
+def count_bits(n)
+    ans = []
+    for i in 0..n
+        num_of_set_bits = 0
+        while i>0
+            pow = Math.log(i,2).to_int
+            i-=(2**pow)
+            num_of_set_bits+=1
+        end
+        ans.push(num_of_set_bits)
+    end
+    ans
+end
+
+# Solution 2 (O(n))
+# Approach: Left shift or right shift doesn't change num of bits in even numbers it only halves the number
+def count_bits(n)
+    bits_count = [0]*(n+1)
+    return bits_count unless n>0
+    bits_count[1]=1
+    for i in 2..n
+        bits_count[i] = bits_count[i/2]
+        bits_count[i]+=1 unless i%2==0
+    end
+    bits_count
+end
+
+#Solution 3 (O(n))
+def count_bits(n)
+    bits_count = [0]*(n+1)
+    return bits_count unless n>0
+    bits_count[1]=1
+    for i in 2..n
+        # replaced division with right shift and condition with bitwise and op with 1
+        bits_count[i] = bits_count[i>>1]+(i&1) 
+    end
+    bits_count
+end
+

Diff for: leetcode/grind75/maximum_subarray_sum.rb

@@ -0,0 +1,19 @@
+=begin
+Given an integer array nums,
+find the subarray with the largest sum, and return its sum.
+=end
+
+# Solution 1 (Kadane's Algorithm)
+def max_sub_array(nums)
+    max_sum = nums[0]
+    curr_sum = 0
+    nums.each do |num|
+        curr_sum=0 if curr_sum<0
+        curr_sum+=num
+        max_sum = curr_sum if curr_sum>max_sum
+    end
+    max_sum
+end
+
+# Solution 2 (Using Dynamic Programming)
+#TO DO

Diff for: leetcode/grind75/same_tree.rb

@@ -0,0 +1,22 @@
+=begin
+Given the roots of two binary trees p and q, write a function to check if they are the same or not.
+Two binary trees are considered the same if they are structurally identical, and the nodes have the same value.
+=end
+
+# Solution (using recursion)
+
+# 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
+
+def is_same_tree(p, q)
+    return true if p.nil? and q.nil?
+    return false if  p.nil? or q.nil? or (p.val!=q.val)
+    is_same_tree(p.left,q.left) and is_same_tree(p.right,q.right)
+end