Add 2021 day 06 cpp

Author: vss2sn

2021/README.md

@@ -9,3 +9,4 @@ This folder contains solutions to each of the problems in Advent of Code 2021 in
 | <nobr> [Day 3: Binary Diagnostic](https://adventofcode.com/2021/day/3) </nobr> | <nobr> [Part 1](/2021/cpp/day_03a.cpp) [Part 2](/2021/cpp/day_03b.cpp) </nobr> | </nobr> [Link](/2021/input/day_03_input) </nobr> | </nobr> [Link](/2021/sample_input/day_03_sample_input) </nobr> | </nobr> [Link](/2021/puzzles/day_03_puzzle) </nobr> |
 | <nobr> [Day 4: Giant Squid](https://adventofcode.com/2021/day/4) </nobr> | <nobr> [Part 1](/2021/cpp/day_04a.cpp) [Part 2](/2021/cpp/day_04b.cpp) </nobr> | </nobr> [Link](/2021/input/day_04_input) </nobr> | </nobr> [Link](/2021/sample_input/day_04_sample_input) </nobr> | </nobr> [Link](/2021/puzzles/day_04_puzzle) </nobr> |
 | <nobr> [Day 5: Hydrothermal Venture](https://adventofcode.com/2021/day/5) </nobr> | <nobr> [Part 1](/2021/cpp/day_05a.cpp) [Part 2](/2021/cpp/day_05b.cpp) </nobr> | </nobr> [Link](/2021/input/day_05_input) </nobr> | </nobr> [Link](/2021/sample_input/day_05_sample_input) </nobr> | </nobr> [Link](/2021/puzzles/day_05_puzzle) </nobr> |
+| <nobr> [Day 6: Lanternfish](https://adventofcode.com/2021/day/6) </nobr> | <nobr> [Part 1](/2021/cpp/day_06a.cpp) [Part 2](/2021/cpp/day_06b.cpp) </nobr> | </nobr> [Link](/2021/input/day_06_input) </nobr> | </nobr> [Link](/2021/sample_input/day_06_sample_input) </nobr> | </nobr> [Link](/2021/puzzles/day_06_puzzle) </nobr> |

2021/cpp/day_06a.cpp

@@ -0,0 +1,48 @@
+#include <fstream>
+#include <iostream>
+#include <string>
+#include <vector>
+
+void print(const std::vector<int>& v) {
+  for (const auto ele : v) {
+    std::cout << ele << ',';
+  }
+  std::cout << '\n';
+}
+
+int main(int argc, char * argv[]) {
+  std::string input = "../input/day_06_input";
+  if (argc > 1) {
+    input = argv[1];
+  }
+
+  std::string line;
+  std::fstream file(input);
+  std::getline(file, line);
+  std::vector<int> fish;
+  std::size_t start = 0;
+  std::size_t end = line.find(',', start);
+  while (end != std::string::npos) {
+    fish.emplace_back(std::stoi(line.substr(start, end - start)));
+    start = end + 1;
+    end = line.find(',', start);
+  }
+  fish.emplace_back(std::stoi(line.substr(start, line.size() - start)));
+  // print(fish);
+  for (int day = 0; day < 80; day++) {
+    int to_add = 0;
+    for (auto& f : fish) {
+      if (f == 0) {
+          to_add++;
+          f = 7;
+      }
+      f--;
+    }
+    for (int i = 0; i < to_add; i++) {
+      fish.emplace_back(8);
+    }
+    // print(fish);
+  }
+  std::cout << fish.size() << '\n';
+  return 0;
+}

2021/cpp/day_06b.cpp

@@ -0,0 +1,57 @@
+#include <fstream>
+#include <iostream>
+#include <string>
+#include <unordered_map>
+
+void print(const std::unordered_map<int, long long>& m) {
+  for (const auto& p : m) {
+    std::cout << p.first << ": " << p.second << '\n';
+  }
+  std::cout << '\n';
+}
+
+int main(int argc, char * argv[]) {
+  std::string input = "../input/day_06_input";
+  if (argc > 1) {
+    input = argv[1];
+  }
+
+  std::string line;
+  std::fstream file(input);
+  std::getline(file, line);
+  std::size_t start = 0;
+  std::size_t end = line.find(',', start);
+  std::unordered_map<int, long long> fish;
+  for (int i = 0; i < 9; i++) {
+    fish[i] = 0;
+  }
+  while (end != std::string::npos) {
+    const auto val = std::stoll(line.substr(start, end - start));
+    fish[val]++;
+    start = end + 1;
+    end = line.find(',', start);
+  }
+  const auto val = std::stoll(line.substr(start, line.size() - start));
+  fish[val]++;
+  // print(fish);
+
+  for (int day = 0; day < 256; day++) {
+    const long long to_add = fish[0];
+    for (int i = 1; i < 7; i++) {
+      fish[i-1] = fish[i];
+    }
+    fish[6] = to_add + fish[7];
+    fish[7] = fish[8];
+    fish[8] = to_add;
+    // print(fish);
+  }
+
+  // std::cout << "Final numbers" << '\n';
+  // print(fish);
+  long long sum = 0;
+  for (const auto& p : fish) {
+    sum += p.second;
+  }
+  std::cout << sum << '\n';
+  return 0;
+}

2021/sample_input/day_06_sample_input

@@ -0,0 +1 @@
+3,4,3,1,2

README.md

@@ -6,6 +6,6 @@ This repository contains solutions to the Advent of Code puzzles.
 
 | Year | C++ | Python | Link to folders | Link to README.md |
 |:----:|:----:|:----:|:----:|:----:|
-|2021  |1-5 | - | [Link](/2021/) |[Link](/2021/README.md) |
+|2021  |1-6 | - | [Link](/2021/) |[Link](/2021/README.md) |
 |2020  |1-25 |1-25 | [Link](/2020/) |[Link](/2020/README.md) |
 |2019  |1-25 |1-7  | [Link](/2019/) |[Link](/2019/README.md) |