From de2117327e9621d88d82e87c52eb42ef3f11082a Mon Sep 17 00:00:00 2001
From: Eric Mertens <emertens@galois.com>
Date: Wed, 22 Mar 2023 14:02:29 -0700
Subject: [PATCH] fiddle with 2022-12

---
 2022/12.cpp | 47 ++++++++++++++++++++---------------------------
 1 file changed, 20 insertions(+), 27 deletions(-)

diff --git a/2022/12.cpp b/2022/12.cpp
index bd5e6f4..6ac570a 100644
--- a/2022/12.cpp
+++ b/2022/12.cpp
@@ -1,5 +1,6 @@
 #include <cstdint>
 #include <iostream>
+#include <optional>
 #include <set>
 #include <sstream>
 #include <tuple>
@@ -16,55 +17,47 @@ using aocpp::Grid;
 
 namespace {
 
-auto Parse(std::istream & in) -> std::tuple<Coord, Coord, Grid>
+auto Parse(std::istream & in) -> std::tuple<Coord, std::vector<Coord>, Coord, Grid>
 {
-  Coord start {};
+  Coord start1 {};
+  std::vector<Coord> starts2;
   Coord end {};
   auto grid = Grid::Parse(in);
 
   grid.each([&](Coord c, char v) {
     switch (v) {
-      case 'S': grid[c] = 'a'; start = c; break;
+      case 'S': grid[c] = 'a'; start1 = c; break;
       case 'E': grid[c] = 'z'; end   = c; break;
+      case 'a': starts2.push_back(c);     break;
     }
   });
 
-  return {start, end, std::move(grid)};
+  return {start1, std::move(starts2), end, std::move(grid)};
 }
 
-auto Solve(std::vector<Coord> starts, Coord end, Grid const& grid) -> std::int64_t
+auto Solve(std::vector<Coord> starts, Coord end, Grid const& grid) -> std::optional<std::int64_t>
 {
-  std::vector<Coord> prev_layer(std::move(starts));
   std::vector<Coord> next_layer;
   std::set<Coord> seen;
   std::int64_t counter {1};
 
-  while (!prev_layer.empty()) {
-    for (auto here : prev_layer) {
+  while (!starts.empty()) {
+    for (auto here : starts) {
       if (!seen.insert(here).second) continue;
       auto here_height = grid[here];
       for (auto next : {Up(here), Down(here), Left(here), Right(here)}) {
         if (!grid.contains(next)) continue;
-        if (grid[next] - here_height > 1) continue;
+        if (grid[next] - 1 > here_height) continue;
         if (next == end) { return counter; }
         next_layer.push_back(next);
       }
     }
     counter++;
-    prev_layer.clear();
-    std::swap(prev_layer, next_layer);
+    starts.clear();
+    std::swap(starts, next_layer);
   }
 
-  return -1;
-}
-
-auto Part2Starts(Grid const& grid) -> std::vector<Coord>
-{
-    std::vector<Coord> starts;
-    grid.each([&](Coord c, char v) {
-      if (v == 'a') starts.push_back(c);
-    });
-    return starts;
+  return {};
 }
 
 } // namespace
@@ -78,15 +71,15 @@ TEST_SUITE("2022-12 examples") {
       "acctuvwj\n"
       "abdefghi\n"
     };
-    auto [start, end, grid] = Parse(in);
-    CHECK(31 == Solve({start}, end, grid));
-    CHECK(29 == Solve(Part2Starts(grid), end, grid));
+    auto [start1, starts2, end, grid] = Parse(in);
+    CHECK(31 == Solve({start1}, end, grid));
+    CHECK(29 == Solve(std::move(starts2), end, grid));
   }
 }
 
 auto Main(std::istream & in, std::ostream & out) -> void
 {
-  auto const [start, end, grid] = Parse(in);
-  out << "Part 1: " << Solve({start}, end, grid) << std::endl;
-  out << "Part 2: " << Solve(Part2Starts(grid), end, grid) << std::endl;
+  auto [start1, starts2, end, grid] = Parse(in);
+  out << "Part 1: " << Solve({start1}, end, grid).value_or(-1) << std::endl;
+  out << "Part 2: " << Solve(std::move(starts2), end, grid).value_or(-1) << std::endl;
 }