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Implement day 16 part 2.

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Bert Peters
2019-12-16 08:30:17 +01:00
parent a5a0e6f860
commit c46f0f9e2e
1 changed files with 16 additions and 7 deletions
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23
2019/src/day16.cpp
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@@ -26,6 +26,16 @@ namespace {
return result;
}
std::vector<int> partial_sum(const std::vector<int> &numbers) {
std::vector<int> partial_sums(numbers.size());
partial_sums[0] = numbers[0];
for (int j = 1; j < numbers.size(); ++j) {
partial_sums[j] = partial_sums[j - 1] + numbers[j];
}
return partial_sums;
}
std::vector<int> advance(const std::vector<int>& numbers) {
std::vector<int> new_numbers;
new_numbers.reserve(numbers.size());
@@ -91,18 +101,17 @@ void aoc2019::day16_part2(std::istream &input, std::ostream &output) {
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> partial_sums = partial_sum(numbers);
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) {
int n = partial_sums.back() - partial_sums[j] + numbers[j];
new_numbers[j] = std::abs(n % 10);
}
for (int j = 0; j < numbers.size(); ++j) {
new_numbers[j] = partial_sums.back() - partial_sums[j] + numbers[j];
}
numbers = new_numbers;
}
std::copy(numbers.begin(), numbers.begin() + 8, std::ostream_iterator<int>(output));
output << std::endl;
}