From 679dd89b879f58c5f9db4d40c150e4d7205dd3ee Mon Sep 17 00:00:00 2001
From: Eric Mertens <emertens@galois.com>
Date: Tue, 8 Nov 2022 09:50:21 -0800
Subject: [PATCH] chunk in place

---
 2019/08.cpp | 57 +++++++++++++++++++++--------------------------------
 1 file changed, 23 insertions(+), 34 deletions(-)

diff --git a/2019/08.cpp b/2019/08.cpp
index cd71a24..471dbb7 100644
--- a/2019/08.cpp
+++ b/2019/08.cpp
@@ -4,51 +4,39 @@
 #include <iostream>
 #include <iterator>
 #include <vector>
+#include <string_view>
 
 #include <aocpp/Startup.hpp>
 
 namespace {
 
-using Layer = std::array<char, 150>;
-
-auto SplitLayers(std::istream & in) {
-  std::string line;
-  std::getline(in, line);
-
-  std::vector<Layer> layers;
-
-  auto it = line.begin();
-  auto layer_n = line.size() / 150;
-  for (std::size_t layer = 0; layer < layer_n; layer++) {
-    layers.push_back({});
-    for (std::size_t y = 0; y < 150; y++) {
-      layers.back()[y] = *it++;
-    }
-  }
-  return layers;
-}
-
-auto Part1(std::vector<Layer> const& layers) {
+auto Part1(std::string const& line) {
   std::size_t part1 = 0;
-  std::size_t seen = std::numeric_limits<std::size_t>::max();
-  for (auto & layer : layers) {
-    auto zeros = std::count(layer.begin(), layer.end(), '0');
+  auto seen = std::numeric_limits<std::size_t>::max();
+  for (auto it = line.begin();
+       std::distance(it, line.end()) >= 150;
+       std::advance(it, 150))
+  {
+    auto zeros = std::count(it, it + 150, '0');
     if (zeros < seen) {
       seen = zeros;
       part1
-        = std::count(layer.begin(), layer.end(), '1')
-        * std::count(layer.begin(), layer.end(), '2');
+        = std::count(it, it + 150, '1')
+        * std::count(it, it + 150, '2');
     }
   }
   return part1;
 }
 
-auto Flatten(std::vector<Layer> const& layers) {
-  Layer merged {};
+auto Flatten(std::string const& line) {
+  std::string merged(150, ' ');
   for (std::size_t i = 0; i < 150; i++) {
-    for (auto & layer : layers) {
-      if ('2' != layer[i]) {
-        merged[i] = layer[i];
+    for (auto it = line.begin();
+         std::distance(it, line.end()) >= 150;
+         std::advance(it, 150))
+    {
+      if ('2' != it[i]) {
+        merged[i] = it[i];
         break;
       }
     }
@@ -56,7 +44,7 @@ auto Flatten(std::vector<Layer> const& layers) {
   return merged;
 }
 
-auto Draw(Layer picture) {
+auto Draw(std::string const& picture) {
   for (std::size_t y = 0; y < 6; y++) {
     for (std::size_t x = 0; x < 25; x++) {
       std::cout << ('1' == picture[y*25+x] ? "▓" : "░");
@@ -68,7 +56,8 @@ auto Draw(Layer picture) {
 } // namespace
 
 auto main(int argc, char** argv) -> int {
-  auto layers = SplitLayers(aocpp::Startup(argc, argv));
-  std::cout << "Part 1: " << Part1(layers) << std::endl;
-  Draw(Flatten(layers));
+  std::string line;
+  std::getline(aocpp::Startup(argc, argv), line);
+  std::cout << "Part 1: " << Part1(line) << std::endl;
+  Draw(Flatten(line));
 }