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Add 2017 day 20 cpp
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‎2017/README.md

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@@ -27,12 +27,12 @@ This folder contains solutions to each of the problems in Advent of Code 2017 in
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| <nobr> [Day 17: Spinlock](https://adventofcode.com/2017/day/17) </nobr> | <nobr> [Part 1](/2017/cpp/day_17a.cpp) [Part 2](/2017/cpp/day_17b.cpp) </nobr> |[Link](/2017/input/day_17_input)|[Link](/2017/sample_input/day_17_sample_input)|[Link](/2017/puzzles/day_17_puzzle)|
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| <nobr> [Day 18: Duet](https://adventofcode.com/2017/day/18) </nobr> | <nobr> [Part 1](/2017/cpp/day_18a.cpp) [Part 2](/2017/cpp/day_18b.cpp) </nobr> |[Link](/2017/input/day_18_input)|[Link](/2017/sample_input/day_18_sample_input)|[Link](/2017/puzzles/day_18_puzzle)|
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| <nobr> [Day 19: A Series of Tubes](https://adventofcode.com/2017/day/19) </nobr> | <nobr> [Part 1](/2017/cpp/day_19a.cpp) [Part 2](/2017/cpp/day_19b.cpp) </nobr> |[Link](/2017/input/day_19_input)|[Link](/2017/sample_input/day_19_sample_input)|[Link](/2017/puzzles/day_19_puzzle)|
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| <nobr> [Day 20: Particle Swarm](https://adventofcode.com/2017/day/20) </nobr> | <nobr> [Part 1](/2017/cpp/day_20a.cpp) [Part 2](/2017/cpp/day_20b.cpp) </nobr> |[Link](/2017/input/day_20_input)|[Link](/2017/sample_input/day_20_sample_input)|[Link](/2017/puzzles/day_20_puzzle)|
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#### TODO ####
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|Puzzle|C++ Solutions|Input|Sample Input|Puzzle page with solutions|
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|:---:|:---:|:---:|:---:|:---:|
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| <nobr> [Day 20: ](https://adventofcode.com/2017/day/20) </nobr> | <nobr> [Part 1](/2017/cpp/day_20a.cpp) [Part 2](/2017/cpp/day_20b.cpp) </nobr> |[Link](/2017/input/day_20_input)|[Link](/2017/sample_input/day_20_sample_input)|[Link](/2017/puzzles/day_20_puzzle)|
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| <nobr> [Day 21: ](https://adventofcode.com/2017/day/21) </nobr> | <nobr> [Part 1](/2017/cpp/day_21a.cpp) [Part 2](/2017/cpp/day_21b.cpp) </nobr> |[Link](/2017/input/day_21_input)|[Link](/2017/sample_input/day_21_sample_input)|[Link](/2017/puzzles/day_21_puzzle)|
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| <nobr> [Day 22: ](https://adventofcode.com/2017/day/22) </nobr> | <nobr> [Part 1](/2017/cpp/day_22a.cpp) [Part 2](/2017/cpp/day_22b.cpp) </nobr> |[Link](/2017/input/day_22_input)|[Link](/2017/sample_input/day_22_sample_input)|[Link](/2017/puzzles/day_22_puzzle)|
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| <nobr> [Day 23: ](https://adventofcode.com/2017/day/23) </nobr> | <nobr> [Part 1](/2017/cpp/day_23a.cpp) [Part 2](/2017/cpp/day_23b.cpp) </nobr> |[Link](/2017/input/day_23_input)|[Link](/2017/sample_input/day_23_sample_input)|[Link](/2017/puzzles/day_23_puzzle)|

‎2017/cpp/day_20a.cpp

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#include <algorithm>
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#include <fstream>
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#include <iostream>
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#include <string>
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#include <limits>
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#include <unordered_map>
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#include <unordered_set>
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#include <vector>
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#include <regex>
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struct Coord3D {
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int x;
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int y;
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int z;
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int dist () const {
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return std::abs(x) + std::abs(y) + std::abs(z);
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}
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int sum () const {
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return x + y + z;
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}
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Coord3D operator + (const Coord3D& c) {
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Coord3D ans;
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ans.x = x + c.x;
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ans.y = y + c.y;
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ans.z = z + c.z;
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return ans;
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}
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Coord3D operator += (const Coord3D& c) {
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x += c.x;
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y += c.y;
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z += c.z;
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return *this;
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}
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};
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int dot_product(const Coord3D& v0, const Coord3D& v1) {
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return v0.x * v1.x + v0.y * v1.y + v0.z * v1.z;
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}
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struct Particle {
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Coord3D p;
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Coord3D v;
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Coord3D a;
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};
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int main(int argc, char* argv[]) {
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const std::string input = (argc > 1) ? argv[1] : "../input/day_20_input" ;
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std::ifstream file(input);
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std::string line;
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const std::regex pattern(R"(p=<(-?[0-9]+),(-?[0-9]+),(-?[0-9]+)>, v=<(-?[0-9]+),(-?[0-9]+),(-?[0-9]+)>, a=<(-?[0-9]+),(-?[0-9]+),(-?[0-9]+)>)");
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std::vector<Particle> particles;
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int min_acc = std::numeric_limits<int>::max();
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std::vector<int> particles_with_min_acc;
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// Find all particles with the minimum acceleration
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// as at t-> infinity, those will be the closest
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while(std::getline(file, line)) {
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std::smatch match;
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std::regex_search(line, match, pattern);
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Particle particle;
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particle.p.x = std::stoi(match[1]);
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particle.p.y = std::stoi(match[2]);
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particle.p.z = std::stoi(match[3]);
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particle.v.x = std::stoi(match[4]);
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particle.v.y = std::stoi(match[5]);
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particle.v.z = std::stoi(match[6]);
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particle.a.x = std::stoi(match[7]);
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particle.a.y = std::stoi(match[8]);
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particle.a.z = std::stoi(match[9]);
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particles.push_back(particle);
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if (particle.a.dist() < min_acc) {
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particles_with_min_acc.clear();
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particles_with_min_acc.push_back(particles.size()-1);
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min_acc = particle.a.dist();
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} else if (particle.a.dist() == min_acc) {
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particles_with_min_acc.push_back(particles.size()-1);
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}
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}
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// If particles have the same acceleration,
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// Find the time at which each is closest to the origin
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// Get the latest time
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// Check the other particles' distances
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// Lowest distance at the final time
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int ans = particles_with_min_acc[0];
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int min_dist = std::numeric_limits<int>::max();
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int time = 0;
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while (std::any_of(
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std::begin(particles_with_min_acc),
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std::end(particles_with_min_acc),
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[&particles](const int idx) {
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const auto& particle = particles[idx];
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return dot_product(particle.p, particle.v) < 0 || dot_product(particle.p, particle.a) < 0;
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})) {
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for (const auto idx : particles_with_min_acc) {
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auto& particle = particles[idx];
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if (min_dist > particle.p.dist()) {
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// std::cout << idx << " is closest at time " << time << '\n';
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min_dist = particle.p.dist();
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ans = idx;
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}
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particle.p = particle.p + particle.v;
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particle.v = particle.v + particle.a;
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}
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time++;
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}
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std::cout << ans << '\n';
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return 0;
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}

‎2017/cpp/day_20b.cpp

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#include <algorithm>
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#include <fstream>
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#include <iostream>
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#include <string>
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#include <limits>
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#include <unordered_map>
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#include <unordered_set>
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#include <vector>
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#include <cmath>
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#include <regex>
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// Note: increment velocity first, then position (mentioned in part 1 i.e. part a)
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// time: position(time)
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// 0: p(0) = p0
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// 1: p(1) = p0 + v + a
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// 2: p(2) = p0 + v + a + v + 2a
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// n: p(n) = p0 + v + a + ... + v + na = p0 + n * v + n(n+1)/2 * a
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// p(t) = (a * t^2 + (a + 2v) * t + 2 * p0) / 2
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struct Coord3D {
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long long x;
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long long y;
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long long z;
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long long dist () const {
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return std::abs(x) + std::abs(y) + std::abs(z);
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}
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long long sum () const {
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return x + y + z;
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}
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Coord3D operator + (const Coord3D& c) const {
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Coord3D ans;
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ans.x = x + c.x;
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ans.y = y + c.y;
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ans.z = z + c.z;
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return ans;
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}
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Coord3D operator - (const Coord3D& c) const {
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Coord3D ans;
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ans.x = x - c.x;
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ans.y = y - c.y;
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ans.z = z - c.z;
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return ans;
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}
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Coord3D operator += (const Coord3D& c) {
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x += c.x;
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y += c.y;
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z += c.z;
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return *this;
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}
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};
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long long dot_product(const Coord3D& v0, const Coord3D& v1) {
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return v0.x * v1.x + v0.y * v1.y + v0.z * v1.z;
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}
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struct Particle {
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Coord3D p;
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Coord3D v;
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Coord3D a;
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};
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struct Collision {
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long long id0;
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long long id1;
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long long time;
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};
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int find_position_at_time (const int p, const int v, const int a, const int time) {
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// std::cout << "Values: " << s << ' ' << v << ' ' << a << ' ' << time << '\n';
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// std::cout << "Position: " << s + (time + 1 ) * v + (time * time + 1 * a) / 2 << '\n';
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return (a * time * time + (a + 2 * v) * time + 2 * p) / 2;
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}
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std::vector<long long> find_time_of_potential_collision(const int p0, const int p1, const int v0, const int v1, const int a0, const int a1) {
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const auto a = float(a1 - a0);
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float t0 = 0;
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float t1 = 0;
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if (a == 0) {
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t0 = -float(p1 -p0) / float(v1 - v0);
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t1 = -1;
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} else {
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const auto b = float((a1 - a0) + 2 * (v1 - v0));
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const auto c = float(2.f * (p1 - p0));
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// std::cout << "Quad equation values: " << a << ' ' << b << ' ' << c << '\n';
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const auto discriminent_2 = (b * b) - 4 * a *c;
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if (discriminent_2 < 0) {
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// std::cout << "No collision possible; negative b2-4ac" << '\n';
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return {-1, -1};
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}
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// TODO: improve this check
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const auto discriminent = std::sqrt(discriminent_2);
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if (discriminent != int(discriminent)) {
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// std::cout << "No collision possible, not a perfect square: " << discriminent << '\n';
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return {-1, -1};
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}
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t0 = (-b + discriminent) / (2 * a);
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t1 = (-b - discriminent) / (2 * a);
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}
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if (t0 < 0) t0 = -1;
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if (t1 < 0) t1 = -1;
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// std::cout << t0 << ' ' << t1 << '\n';
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if (t0 != int(t0)) t0 = -1;
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if (t1 != int(t1)) t1 = -1;
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// std::cout << "Possible times: " << t0 << ' ' << t1 << '\n';
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return {static_cast<long long>(t0), static_cast<long long>(t1)};
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}
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int main(int argc, char* argv[]) {
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const std::string input = (argc > 1) ? argv[1] : "../input/day_20_input" ;
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std::ifstream file(input);
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std::string line;
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const std::regex pattern(R"(p=<(-?[0-9]+),(-?[0-9]+),(-?[0-9]+)>, v=<(-?[0-9]+),(-?[0-9]+),(-?[0-9]+)>, a=<(-?[0-9]+),(-?[0-9]+),(-?[0-9]+)>)");
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std::vector<Particle> particles;
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long long min_acc = std::numeric_limits<long long>::max();
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while(std::getline(file, line)) {
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std::smatch match;
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std::regex_search(line, match, pattern);
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Particle particle;
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particle.p.x = std::stoi(match[1]);
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particle.p.y = std::stoi(match[2]);
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particle.p.z = std::stoi(match[3]);
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particle.v.x = std::stoi(match[4]);
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particle.v.y = std::stoi(match[5]);
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particle.v.z = std::stoi(match[6]);
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particle.a.x = std::stoi(match[7]);
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particle.a.y = std::stoi(match[8]);
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particle.a.z = std::stoi(match[9]);
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particles.push_back(particle);
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}
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std::vector<Collision> collisions;
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for (int i = 0; i < particles.size(); i++) {
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for (int j = i + 1; j < particles.size(); j++) {
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// std::cout << "\nPair: (" << i << "," << j << "): " << '\n';
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const auto times = find_time_of_potential_collision(particles[i].p.x, particles[j].p.x, particles[i].v.x, particles[j].v.x, particles[i].a.x, particles[j].a.x);
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for (const auto time : times) {
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// std::cout << "Time: " << time << '\n';
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if (time != -1 && find_position_at_time(particles[i].p.y, particles[i].v.y, particles[i].a.y, time)
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== find_position_at_time(particles[j].p.y, particles[j].v.y, particles[j].a.y, time) &&
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find_position_at_time(particles[i].p.z, particles[i].v.z, particles[i].a.z, time)
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== find_position_at_time(particles[j].p.z, particles[j].v.z, particles[j].a.z, time) ) {
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// std::cout << "Collision!!!!!!!!!! Time: " << time << '\n';
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Collision c;
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c.id0 = i;
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c.id1 = j;
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c.time = time;
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collisions.push_back(c);
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}
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}
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}
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}
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std::sort(std::begin(collisions), std::end(collisions), [](const auto& c1, const auto& c2) {return c1.time < c2.time; });
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// for (const auto & c : collisions) {
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// std::cout << c.time << '\n';
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// }
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std::unordered_map<long long, long long> id_to_destruction_time;
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for (const auto& c : collisions) {
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if (id_to_destruction_time.find(c.id0) == id_to_destruction_time.end() && id_to_destruction_time.find(c.id1) == id_to_destruction_time.end()) {
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id_to_destruction_time[c.id0] = c.time;
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id_to_destruction_time[c.id1] = c.time;
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// std::cout << "Adding " << c.id0 << '\n';
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// std::cout << "Adding " << c.id1 << '\n';
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} else if (id_to_destruction_time.find(c.id0) != id_to_destruction_time.end() && id_to_destruction_time[c.id0] == c.time) {
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id_to_destruction_time[c.id1] = c.time;
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// std::cout << "Adding " << c.id1 << '\n';
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} else if (id_to_destruction_time.find(c.id1) != id_to_destruction_time.end() && id_to_destruction_time[c.id1] == c.time) {
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id_to_destruction_time[c.id0] = c.time;
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// std::cout << "Adding " << c.id0 << '\n';
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}
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}
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std::cout << particles.size() - id_to_destruction_time.size() << '\n';
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return 0;
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}
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‎2017/sample_input/day_20_sample_input

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p=< 3,0,0>, v=< 2,0,0>, a=<-1,0,0>
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p=< 4,0,0>, v=< 0,0,0>, a=<-2,0,0>
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p=<-6,0,0>, v=<3,0,0>, a=<0,0,0>
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p=<-4,0,0>, v=<2,0,0>, a=<0,0,0>
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p=<-2,0,0>, v=<1,0,0>, a=<0,0,0>
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p=<4,0,0>, v=<-1,0,0>, a=<-1,0,0>

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