3 files changed, 150 insertions, 2 deletions
diff --git a/src/common/CMakeLists.txt b/src/common/CMakeLists.txt
index aed9bfee7..3045c003c 100644
--- a/src/common/CMakeLists.txt
+++ b/src/common/CMakeLists.txt
@@ -43,7 +43,8 @@ set(common_sources
   spawn.cpp
   threadpool.cpp
   updates.cpp
-  aligned.c)
+  aligned.c
+  combinator.cpp)
 
 if (STACK_TRACE)
   list(APPEND common_sources stack_trace.cpp)
@@ -77,7 +78,8 @@ set(common_private_headers
   stack_trace.h
   threadpool.h
   updates.h
-  aligned.h)
+  aligned.h
+  combinator.h)
 
 monero_private_headers(common
   ${common_private_headers})
diff --git a/src/common/combinator.cpp b/src/common/combinator.cpp
new file mode 100644
index 000000000..cb4fbc908
--- /dev/null
+++ b/src/common/combinator.cpp
@@ -0,0 +1,50 @@
+// Copyright (c) 2018, The Monero Project
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+// Parts of this file are originally copyright (c) 2012-2013 The Cryptonote developers
+
+#include "combinator.h"
+
+namespace tools {
+
+uint64_t combinations_count(uint32_t k, uint32_t n)
+{
+  if (k > n) {
+    throw std::runtime_error("k must not be greater than n");
+  }
+
+  uint64_t c = 1;
+  for (uint64_t i = 1; i <= k; ++i) {
+    c *= n--;
+    c /= i;
+  }
+
+  return c;
+}
+
+}
diff --git a/src/common/combinator.h b/src/common/combinator.h
new file mode 100644
index 000000000..72c6800d5
--- /dev/null
+++ b/src/common/combinator.h
@@ -0,0 +1,96 @@
+// Copyright (c) 2018, The Monero Project
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+// Parts of this file are originally copyright (c) 2012-2013 The Cryptonote developers
+
+#pragma once
+
+#include <iostream>
+#include <vector>
+
+namespace tools {
+
+uint64_t combinations_count(uint32_t k, uint32_t n);
+
+template<typename T>
+class Combinator {
+public:
+  Combinator(const std::vector<T>& v) : origin(v) { }
+
+  std::vector<std::vector<T>> combine(size_t k);
+
+private:
+  void doCombine(size_t from, size_t k);
+
+  std::vector<T> origin;
+  std::vector<std::vector<T>> combinations;
+  std::vector<size_t> current;
+};
+
+template<typename T>
+std::vector<std::vector<T>> Combinator<T>::combine(size_t k)
+{
+  if (k > origin.size())
+  {
+    throw std::runtime_error("k must be smaller than elements number");
+  }
+
+  if (k == 0)
+  {
+    throw std::runtime_error("k must be greater than zero");
+  }
+
+  combinations.clear();
+  doCombine(0, k);
+  return combinations;
+}
+
+template<typename T>
+void Combinator<T>::doCombine(size_t from, size_t k)
+{
+  current.push_back(0);
+
+  for (size_t i = from; i <= origin.size() - k; ++i)
+  {
+    current.back() = i;
+
+    if (k > 1) {
+      doCombine(i + 1, k - 1);
+    } else {
+      std::vector<T> comb;
+      for (auto ind: current) {
+        comb.push_back(origin[ind]);
+      }
+      combinations.push_back(comb);
+    }
+  }
+
+  current.pop_back();
+}
+
+} //namespace tools