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Day 16 part 1: optimize all but initial allocations.

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I don't think this can be much faster.
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Bert Peters
2019-12-16 23:02:53 +01:00
parent 36c1692916
commit 77b1728397
1 changed files with 24 additions and 30 deletions
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54
2019/src/day16.cpp
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@@ -3,7 +3,9 @@
#include <vector> #include <vector>
#include <cassert> #include <cassert>
#include <iterator> #include <iterator>
#include <numeric>
#include "days.hpp" #include "days.hpp"
#include "utils.hpp"
namespace { namespace {
std::array<int, 4> base_pattern{0, 1, 0, -1}; std::array<int, 4> base_pattern{0, 1, 0, -1};
@@ -26,47 +28,38 @@ namespace {
return result; return result;
} }
std::vector<int> partial_sum(const std::vector<int> &numbers) { void simulate(std::vector<int> numbers, std::ostream &output) {
std::vector<int> new_numbers(numbers.size());
std::vector<int> partial_sums(numbers.size()); 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; for (int i = 0; i < 100; ++i) {
} for (int rank = 0; rank < numbers.size(); ++rank) {
std::partial_sum(numbers.begin() + rank, numbers.end(), partial_sums.begin() + rank);
void next_phase(const std::vector<int>& numbers, std::vector<int> &new_numbers) { int n = 0;
new_numbers.resize(numbers.size()); for (int pos = rank; pos < numbers.size(); pos += rank + 1) {
int run = std::min(rank + 1, (int) numbers.size() - pos);
for (int rank = 0; rank < numbers.size(); ++rank) { if (int modifier = get_modifier(rank, pos); modifier) {
auto partial_sums = partial_sum(numbers); n += modifier * (partial_sums[pos + run - 1] - partial_sums[pos] + numbers[pos]);
int n = 0; }
for (int pos = rank; pos < numbers.size(); pos += rank + 1) {
int run = std::min(rank + 1, (int) numbers.size() - pos);
if (int modifier = get_modifier(rank, pos); modifier) {
n += modifier * (partial_sums[pos + run - 1] - partial_sums[pos] + numbers[pos]);
} }
n = std::abs(n % 10);
new_numbers[rank] = n;
} }
n = std::abs(n % 10); std::swap(numbers, new_numbers);
new_numbers[rank] = n;
} }
std::copy(numbers.begin(), numbers.begin() + 8, std::ostream_iterator<int>(output));
output << std::endl;
} }
} }
void aoc2019::day16_part1(std::istream &input, std::ostream &output) { void aoc2019::day16_part1(std::istream &input, std::ostream &output) {
auto numbers = read_input(input); auto numbers = read_input(input);
auto new_numbers = numbers;
for (int i = 0; i < 100; ++i) { simulate(std::move(numbers), output);
next_phase(numbers, new_numbers);
std::swap(numbers, new_numbers);
}
std::copy(numbers.begin(), numbers.begin() + 8, std::ostream_iterator<int>(output));
output << std::endl;
} }
void aoc2019::day16_part2(std::istream &input, std::ostream &output) { void aoc2019::day16_part2(std::istream &input, std::ostream &output) {
@@ -89,9 +82,10 @@ void aoc2019::day16_part2(std::istream &input, std::ostream &output) {
numbers = std::vector(numbers.begin() + offset, numbers.end()); numbers = std::vector(numbers.begin() + offset, numbers.end());
std::vector<int> new_numbers(numbers.size()); std::vector<int> new_numbers(numbers.size());
std::vector<int> partial_sums(numbers.size());
for (int i = 0; i < 100; ++i) { for (int i = 0; i < 100; ++i) {
std::vector<int> partial_sums = partial_sum(numbers); std::partial_sum(numbers.begin(), numbers.end(), partial_sums.begin());
for (int j = 0; j < numbers.size(); ++j) { for (int j = 0; j < numbers.size(); ++j) {
int n = partial_sums.back() - partial_sums[j] + numbers[j]; int n = partial_sums.back() - partial_sums[j] + numbers[j];