New cpp folder structure

Signed-off-by: Alexander Borsuk <me@alex.bio>

libs/base/set_operations.hpp

@@ -0,0 +1,31 @@
+#pragma once
+
+// Similar to set_difference(), but if element is present n times in the first sequence and once in
+// the second sequence, all n copies are filtered, insted of one.
+template<typename Iter1T, typename Iter2T, typename OutIterT, typename LessT>
+OutIterT SetDifferenceUnlimited(Iter1T beg1, Iter1T end1,
+                                Iter2T beg2, Iter2T end2,
+                                OutIterT out, LessT lessCompare)
+  {
+    while (beg1 != end1 && beg2 != end2)
+    {
+      if (lessCompare(*beg1, *beg2))
+      {
+        *out = *beg1;
+        ++beg1;
+        ++out;
+      }
+      else if (lessCompare(*beg2, *beg1))
+      {
+        ++beg2;
+      }
+      else
+      {
+        ++beg1;
+        // This is the difference between set_difference and this function:
+        // In set_difference the commented line should be present.
+        // ++beg2;
+      }
+    }
+    return std::copy(beg1, end1, out);
+  }