Add 2021 day 7 puzzles

2021/puzzle-07-01.cc

@@ -0,0 +1,44 @@
+//
+// Created by Matthew Gretton-Dann on 07/12/2021.
+//
+
+#include <iostream>
+#include <limits>
+#include <numeric>
+#include <string>
+#include <vector>
+
+auto main() -> int
+{
+  std::vector<unsigned> crabs;
+  std::string line;
+  while (std::getline(std::cin, line)) {
+    std::size_t idx{0};
+    while (idx < line.size()) {
+      if (line[idx] == ',') {
+        ++idx;
+      }
+      else {
+        std::size_t end{0};
+        crabs.emplace_back(std::stoul(line.substr(idx), &end));
+        idx += end;
+      }
+    }
+  }
+
+  unsigned min_pos{0};
+  unsigned min_fuel{std::numeric_limits<unsigned>::max()};
+  auto [low_crab, high_crab] = std::minmax_element(crabs.begin(), crabs.end());
+  for (auto pos{*low_crab}; pos <= *high_crab; ++pos) {
+    auto fuel{std::accumulate(crabs.begin(), crabs.end(), unsigned{0}, [pos](auto a, auto b) {
+      return a + ((b > pos) ? (b - pos) : (pos - b));
+    })};
+    if (fuel < min_fuel) {
+      min_fuel = fuel;
+      min_pos = pos;
+    }
+  }
+
+  std::cout << "Minimum fuel = " << min_fuel << " at position " << min_pos << '\n';
+  return 0;
+}

2021/puzzle-07-02.cc

@@ -0,0 +1,45 @@
+//
+// Created by Matthew Gretton-Dann on 07/12/2021.
+//
+
+#include <iostream>
+#include <limits>
+#include <numeric>
+#include <string>
+#include <vector>
+
+auto main() -> int
+{
+  std::vector<unsigned> crabs;
+  std::string line;
+  while (std::getline(std::cin, line)) {
+    std::size_t idx{0};
+    while (idx < line.size()) {
+      if (line[idx] == ',') {
+        ++idx;
+      }
+      else {
+        std::size_t end{0};
+        crabs.emplace_back(std::stoul(line.substr(idx), &end));
+        idx += end;
+      }
+    }
+  }
+
+  unsigned min_pos{0};
+  unsigned min_fuel{std::numeric_limits<unsigned>::max()};
+  auto [low_crab, high_crab] = std::minmax_element(crabs.begin(), crabs.end());
+  for (auto pos{*low_crab}; pos <= *high_crab; ++pos) {
+    auto fuel{std::accumulate(crabs.begin(), crabs.end(), unsigned{0}, [pos](auto a, auto b) {
+      unsigned dist{(b > pos) ? (b - pos) : (pos - b)};
+      return a + (dist * (dist + 1)) / 2;
+    })};
+    if (fuel < min_fuel) {
+      min_fuel = fuel;
+      min_pos = pos;
+    }
+  }
+
+  std::cout << "Minimum fuel = " << min_fuel << " at position " << min_pos << '\n';
+  return 0;
+}