Add day7 in C++

day7.h

@@ -0,0 +1,89 @@
+#include <algorithm>
+#include <fstream>
+#include <optional>
+#include <vector>
+
+namespace {
+  using namespace std;
+
+  vector<int> parse(ifstream input) {
+    vector<int> program;
+    int value;
+    while (input >> value) {
+      program.push_back(value);
+      input.ignore(1, ',');
+    }
+    return program;
+  }
+
+  pair<optional<int>, bool> run(int& pos, vector<int>& program, optional<int> input) {
+    optional<int> output;
+    for (int op; (op = program[pos] % 100) != 3 || input;) {
+      auto param = [&, mode = program[pos++] / 10]() mutable -> int& {
+        mode /= 10;
+        if (mode % 10 == 0)
+          return program[program[pos++]];
+        if (mode % 10 == 1)
+          return program[pos++];
+      };
+      if (op == 1) {
+        param() = param() + param();
+      } else if (op == 2) {
+        param() = param() * param();
+      } else if (op == 3) {
+        param() = *input;
+        input.reset();
+      } else if (op == 4) {
+        output = param();
+      } else if (op == 5) {
+        pos = param() != 0 ? param() : pos + 1;
+      } else if (op == 6) {
+        pos = param() == 0 ? param() : pos + 1;
+      } else if (op == 7) {
+        int left = param();
+        param() = left < param() ? 1 : 0;
+      } else if (op == 8) {
+        param() = param() == param() ? 1 : 0;
+      } else if (op == 99) {
+        return { output, true };
+      }
+    }
+    return { output, false };
+  };
+
+  int loop(const vector<int>& program, const vector<int>& phases) {
+    bool halted = false;
+    vector<pair<int, vector<int>>> states;
+    for (int phase : phases) {
+      auto& state = states.emplace_back(0, program);
+      tie(ignore, halted) = run(state.first, state.second, phase);
+    }
+    optional<int> output = 0;
+    while (!halted) {
+      for (auto& [pos, program] : states) {
+        tie(output, halted) = run(pos, program, output);
+      }
+    }
+    return *output;
+  }
+
+  int part1(ifstream input) {
+    auto program = parse(move(input));
+    vector<int> phases { 0, 1, 2, 3, 4 };
+    int maximum = 0;
+    do {
+      maximum = max(maximum, loop(program, phases));
+    } while (next_permutation(begin(phases), end(phases)));
+    return maximum;
+  }
+
+  int part2(ifstream input) {
+    auto program = parse(move(input));
+    vector<int> phases { 5, 6, 7, 8, 9 };
+    int maximum = 0;
+    do {
+      maximum = max(maximum, loop(program, phases));
+    } while (next_permutation(begin(phases), end(phases)));
+    return maximum;
+  }
+}