Add Ruby Sieve of Sundaram snippet

Author: ACR1209

snippets/ruby/math-and-numbers/calculate-compound-interest.md

@@ -6,7 +6,7 @@ contributors: axorax
 tags: ruby,math,compound interest,finance
 ---
 
-```ruby
+```rb
 def compound_interest(principal, rate, time, n = 1)
     principal * (1 + rate / n) ** (n * time)
 end

snippets/ruby/math-and-numbers/sieve-of-sundaram.md

@@ -0,0 +1,31 @@
+---
+title: Find all primes up to integer (Sieve of Sundaram)
+description: Finds all the prime numbers up to a specific integer.
+author: ACR1209
+tags: ruby,math,prime numbers
+---
+
+```rb
+def sieve_of_sundaram(limit)
+    n = (limit - 1) / 2
+    marked = Array.new(n + 1, false)
+
+    (1..n).each do |i|
+        j = i
+        while (i + j + 2 * i * j) <= n
+            marked[i + j + 2 * i * j] = true
+            j += 1
+        end
+    end
+
+    primes = [2]
+    (1..n).each do |i|
+        primes << (2 * i + 1) unless marked[i]
+    end
+
+    primes
+end
+
+# Usage:
+print sieve_of_sundaram(30) # Output: [2, 3, 5, 7, 11, 13, 17, 19, 23, 29]
+```