diff --git a/2022/20.cpp b/2022/20.cpp
new file mode 100644
index 0000000..a40c0fa
--- /dev/null
+++ b/2022/20.cpp
@@ -0,0 +1,115 @@
+#include <algorithm>
+#include <cstdint>
+#include <iostream>
+#include <iterator>
+#include <numeric>
+#include <sstream>
+#include <string>
+#include <tuple>
+#include <vector>
+
+#include <doctest.h>
+
+#include <aocpp/DivMod.hpp>
+#include <aocpp/Startup.hpp>
+
+namespace {
+
+using Input = std::vector<std::int64_t>;
+
+/// @brief Parse the input stream as a newline-delimited list of lists of integers
+/// @param in input file parsed until EOF
+/// @return outer list of elves, inner lists of calories
+auto Parse(std::istream & in) -> Input
+{
+  Input result;
+  using It = std::istream_iterator<std::int64_t>;
+  std::copy<It>(in, {}, std::back_inserter(result));
+  return result;
+}
+
+auto Solve(Input const& input, std::size_t const rounds) -> std::int64_t
+{
+  std::size_t const len = input.size();
+  std::vector<std::size_t> fwds(len), bwds(len);
+
+  for (std::size_t i = 0; i < len; ++i) {
+    fwds[i] = aocpp::Mod<std::int64_t>(i+1, len);
+    bwds[i] = aocpp::Mod<std::int64_t>(i-1, len);
+  }
+
+  for (std::size_t r = 0; r < rounds; ++r) {
+    for (std::size_t i = 0; i < len; ++i) {
+      
+      // Remove i from the ring
+      auto next = fwds[i];
+      auto prev = bwds[i];
+      fwds[prev] = next;
+      bwds[next] = prev;
+
+      auto const steps = aocpp::Mod<std::int64_t>(input[i], len - 1);
+      if (steps < len/2) {
+        for (std::size_t s = 0; s < steps; ++s) {
+          next = fwds[next];
+        }
+      } else {
+        for (std::size_t s = 0; s < len - 1 - steps; ++s) {
+          next = bwds[next];
+        }
+      }
+      prev = bwds[next];
+
+      // insert i into the ring
+      fwds[i] = next;
+      bwds[i] = prev;
+      fwds[prev] = i;
+      bwds[next] = i;
+    }
+  }
+
+  std::int64_t sum {0};
+  auto cursor = std::distance(input.begin(), std::find(input.begin(), input.end(), 0));
+  for (std::size_t r = 0; r < 3; ++r) {
+    for (std::size_t s = 0; s < 1000; ++s) {
+      cursor = fwds[cursor];
+    }
+    sum += input[cursor];
+  }
+
+  return sum;
+}
+
+auto Part1(Input const& input) -> std::int64_t
+{
+  return Solve(input, 1);
+}
+
+auto Part2(Input input) -> std::int64_t
+{
+  for (auto& x : input) { x *= 811589153; }
+  return Solve(input, 10);
+}
+
+} // namespace
+
+TEST_SUITE("2022-20 examples") {
+  TEST_CASE("example") {
+    std::istringstream in {
+      "1\n"
+      "2\n"
+      "-3\n"
+      "3\n"
+      "-2\n"
+      "0\n"
+      "4\n"};
+      auto input = Parse(in);
+      CHECK(3 == Part1(input));
+      CHECK(1623178306 == Part2(input));
+  }
+}
+
+auto main(int argc, char** argv) -> int {
+  auto input = Parse(*aocpp::Startup(argc, argv));
+  std::cout << "Part 1: " << Part1(input) << std::endl;
+  std::cout << "Part 2: " << Part2(input) << std::endl;
+}
diff --git a/2022/25.cpp b/2022/25.cpp
index 1f6db08..f508a19 100644
--- a/2022/25.cpp
+++ b/2022/25.cpp
@@ -9,25 +9,14 @@
 
 #include <doctest.h>
 
+#include <aocpp/DivMod.hpp>
 #include <aocpp/Startup.hpp>
 
 namespace {
 
+using aocpp::DivMod;
 using It = std::istream_iterator<std::string>;
 
-// 
-template <typename T>
-auto DivMod(T dividend, T divisor) -> std::pair<T, T>
-{
-  auto const quotient  = dividend / divisor;
-  auto const remainder = dividend % divisor;
-  if (remainder == 0 || (remainder > 0) == (divisor > 0)) {
-    return {quotient, remainder};
-  } else {
-    return {quotient - 1, remainder + divisor};
-  }
-}
-
 template <typename T>
 auto FromInt(T x) -> std::string
 {
@@ -96,18 +85,6 @@ TEST_SUITE("2022-25 examples") {
     CHECK(FromInt(-7) == "-=");
     CHECK(FromInt(-11) == "=-");
   }
-
-  TEST_CASE("DivMod behavior") {
-    CHECK(DivMod<int>(2,5) == std::make_pair(0,2));
-    CHECK(DivMod<int>(-2,5) == std::make_pair(-1,3));
-    CHECK(DivMod<int>(2,-5) == std::make_pair(-1,-3));
-    CHECK(DivMod<int>(-2,-5) == std::make_pair(0,-2));
-    
-    CHECK(DivMod<int>(-5,-5) == std::make_pair(1,0));
-    CHECK(DivMod<int>(-5,5) == std::make_pair(-1,0));
-    CHECK(DivMod<int>(5,-5) == std::make_pair(-1,0));
-    CHECK(DivMod<int>(-5,-5) == std::make_pair(1,0));
-  }
 }
 
 auto main(int argc, char** argv) -> int
diff --git a/2022/CMakeLists.txt b/2022/CMakeLists.txt
index 9e8cbb9..0857755 100644
--- a/2022/CMakeLists.txt
+++ b/2022/CMakeLists.txt
@@ -13,5 +13,8 @@ target_link_libraries(2022_12 aocpp)
 add_executable(2022_18 18.cpp)
 target_link_libraries(2022_18 aocpp)
 
+add_executable(2022_20 20.cpp)
+target_link_libraries(2022_20 aocpp)
+
 add_executable(2022_25 25.cpp)
 target_link_libraries(2022_25 aocpp)
diff --git a/lib/include/aocpp/DivMod.hpp b/lib/include/aocpp/DivMod.hpp
new file mode 100644
index 0000000..d7e58bf
--- /dev/null
+++ b/lib/include/aocpp/DivMod.hpp
@@ -0,0 +1,50 @@
+#ifndef AOCPP_DIVMOD_HPP_
+#define AOCPP_DIVMOD_HPP_
+
+#include <tuple>
+
+#include "../doctest.h"
+
+namespace aocpp {
+
+template <typename T>
+auto DivMod(T dividend, T divisor) -> std::pair<T, T>
+{
+  auto const quotient  = dividend / divisor;
+  auto const remainder = dividend % divisor;
+  if (remainder == 0 || (remainder > 0) == (divisor > 0)) {
+    return {quotient, remainder};
+  } else {
+    return {quotient - 1, remainder + divisor};
+  }
+}
+
+template <typename T>
+auto Mod(T dividend, T divisor) -> T
+{
+  return DivMod(dividend, divisor).second;
+}
+
+template <typename T>
+auto Div(T dividend, T divisor) -> T
+{
+  return DivMod(dividend, divisor).first;
+}
+
+TEST_SUITE("divmod.hpp") {
+  TEST_CASE("DivMod behavior") {
+    CHECK(DivMod<int>(2,5) == std::make_pair(0,2));
+    CHECK(DivMod<int>(-2,5) == std::make_pair(-1,3));
+    CHECK(DivMod<int>(2,-5) == std::make_pair(-1,-3));
+    CHECK(DivMod<int>(-2,-5) == std::make_pair(0,-2));
+    
+    CHECK(DivMod<int>(-5,-5) == std::make_pair(1,0));
+    CHECK(DivMod<int>(-5,5) == std::make_pair(-1,0));
+    CHECK(DivMod<int>(5,-5) == std::make_pair(-1,0));
+    CHECK(DivMod<int>(-5,-5) == std::make_pair(1,0));
+  }
+}
+
+}
+
+#endif