Merge pull request neetcode-gh#1936 from saip7795/sp/multiply_strings

Create 0043-multiply-strings.rb

ruby/0043-multiply-strings.rb

@@ -0,0 +1,22 @@
+def multiply(num1, num2)
+
+ return "0" if [num1,num2].include?("0")
+
+ res = [0] * (num1.length + num2.length)
+
+ num1.reverse!
+ num2.reverse!
+
+ (0..num1.length-1).each do |i|
+ (0..num2.length-1).each do |j|
+ digit = num1[i].to_i * num2[j].to_i
+ res[i+j] += digit
+ res[i+j+1] += (res[i+j]/10)
+ res[i+j] = res[i+j] % 10
+ end
+ end
+
+ res.reverse!
+
+ return res.join.to_i.to_s
+end