Partial incorrect part 2.

2019/src/day16.cpp

@@ -25,6 +25,24 @@ namespace {
 
         return result;
     }
+
+    std::vector<int> advance(const std::vector<int>& numbers) {
+        std::vector<int> new_numbers;
+        new_numbers.reserve(numbers.size());
+
+        for (int rank = 0; rank < numbers.size(); ++rank) {
+            int n = 0;
+            for (int pos = rank; pos < numbers.size(); ++pos) {
+                n += get_modifier(rank, pos) * numbers[pos];
+            }
+
+            n = std::abs(n % 10);
+
+            new_numbers.push_back(n);
+        }
+
+        return new_numbers;
+    }
 }
 
 void aoc2019::day16_part1(std::istream &input, std::ostream &output) {
@@ -36,7 +54,7 @@ void aoc2019::day16_part1(std::istream &input, std::ostream &output) {
 
         for (int rank = 0; rank < numbers.size(); ++rank) {
             int n = 0;
-            for (int pos = 0; pos < numbers.size(); ++pos) {
+            for (int pos = rank; pos < numbers.size(); ++pos) {
                 n += get_modifier(rank, pos) * numbers[pos];
             }
 
@@ -53,5 +71,38 @@ void aoc2019::day16_part1(std::istream &input, std::ostream &output) {
 }
 
 void aoc2019::day16_part2(std::istream &input, std::ostream &output) {
-    output << "Not implemented\n";
+    auto numbers = read_input(input);
+    const auto initial_size = numbers.size();
+
+    constexpr auto repetitions = 10000;
+
+    numbers.reserve(repetitions * numbers.size());
+
+    int offset = 0;
+    for (int i = 0; i < 7; ++i) {
+        offset *= 10;
+        offset += numbers[i];
+    }
+
+    for (int i = 1; i < repetitions; ++i) {
+        std::copy(numbers.begin(), numbers.begin() + initial_size, std::back_inserter(numbers));
+    }
+
+    numbers = std::vector(numbers.begin() + offset, numbers.end());
+
+    for (int i = 0; i < 100; ++i) {
+        std::vector<int> partial_sums(numbers.size());
+        std::vector<int> new_numbers(numbers.size());
+
+        partial_sums[0] = numbers[0];
+        for (int j = 1; j < numbers.size(); ++j) {
+            partial_sums[j] = partial_sums[j - 1] + numbers[j];
+        }
+
+        for (int j = 0; j < numbers.size(); ++j) {
+            new_numbers[j] = partial_sums.back() - partial_sums[j] + numbers[j];
+        }
+    }
+
+    std::copy(numbers.begin(), numbers.begin() + 8, std::ostream_iterator<int>(output));
 }