2021 day7

3 files changed, 27 insertions, 15 deletions

diff --git a/src/2021/day7/aoc.cpp b/src/2021/day7/aoc.cpp
index 6ba7c29..8bc4607 100644
--- a/src/2021/day7/aoc.cpp
+++ b/src/2021/day7/aoc.cpp
@@ -12,17 +12,24 @@ static void get_number(const char** pp, int* d) {
   *pp = p;
 }
 
-int fuel(int a, const std::map<int, int>& is) {
-  int total{0};
+int crab_move(int x, int y) {
+  int b = std::abs(x - y);
+  return b * (b + 1) / 2;
+}
+
+std::pair<int, int> fuel(int a, const std::map<int, int>& is) {
+  int t0{0};
+  int t1{0};
   for (auto& kv : is) {
     if (kv.first != a) {
-      total += std::abs(a - kv.first) * kv.second;
+      t0 += std::abs(a - kv.first) * kv.second;
+      t1 += crab_move(a, kv.first) * kv.second;
     }
   }
-  return total;
+  return {t0, t1};
 }
 
-int day7(line_view file) {
+std::pair<int, int> day7(line_view file) {
   std::map<int, int> is;
   const char* p1 = file.line;
   const char* p2 = p1 + file.length;
@@ -39,16 +46,19 @@ int day7(line_view file) {
     p1++;
   }
 
-  int min{INT32_MAX};
+  int m1{INT32_MAX};
+  int m2{INT32_MAX};
   for (int i = mi; i <= mx; i++) {
-    int f = fuel(i, is);
-    // printf("%d -> %d\n", i, f);
-    if (f < min) {
-      min = f;
+    auto p = fuel(i, is);
+    // printf("%d -> (%d, %d)\n", i, p.first, p.second);
+    if (p.first < m1) {
+      m1 = p.first;
+    }
+    if (p.second < m2) {
+      m2 = p.second;
     }
   }
-
-  return min;
+  return {m1, m2};
 }
 
 } // namespace aoc2021
diff --git a/src/2021/day7/aoc.h b/src/2021/day7/aoc.h
index 72234fe..6dd69b6 100644
--- a/src/2021/day7/aoc.h
+++ b/src/2021/day7/aoc.h
@@ -3,5 +3,5 @@
 
 namespace aoc2021 {
 
-int day7(line_view);
+std::pair<int, int> day7(line_view);
 }
diff --git a/test/test_2021.cpp b/test/test_2021.cpp
index 405bf03..173542b 100644
--- a/test/test_2021.cpp
+++ b/test/test_2021.cpp
@@ -56,6 +56,8 @@ TEST_CASE("Lanternfish", "[2021]") {
 
 TEST_CASE("The Treachery of Whales", "[2021]") {
   line_view lv = load_file("../src/2021/day7/input");
-  // REQUIRE(37 == aoc2021::day7("16,1,2,0,4,2,7,1,2,14"));
-  REQUIRE(354129 == aoc2021::day7(lv));
+  // auto p = aoc2021::day7("16,1,2,0,4,2,7,1,2,14");
+  auto p = aoc2021::day7(lv);
+  REQUIRE(354129 == p.first);
+  REQUIRE(98905973 == p.second);
 }