105 lines
2.5 KiB
C++
105 lines
2.5 KiB
C++
#include <array>
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#include <bit>
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#include <cstdint>
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#include <iostream>
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#include <optional>
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#include <string>
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#include <vector>
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#include <doctest.h>
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#include <aocpp/Startup.hpp>
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#include <aocpp/Parsing.hpp>
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#include <knothash.hpp>
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namespace {
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using Grid = std::vector<std::array<std::uint8_t, 16>>;
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auto MakeRows(std::string input) -> Grid {
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Grid rows;
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rows.reserve(128);
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input += "-";
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for (int i = 0; i < 128; i++) {
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rows.emplace_back(knothash::hash(input + std::to_string(i)));
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}
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return rows;
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}
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auto CountBits(Grid const& grid) -> std::size_t {
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std::size_t bits = 0;
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for (auto const& row : grid) {
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for (auto const x : row) {
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bits += std::popcount(x);
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}
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}
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return bits;
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}
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auto Connect(std::vector<std::uint16_t> & leaders, std::uint16_t who, std::uint16_t leader) {
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auto who_ = leaders[who];
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if (who_ == std::uint16_t(-1)) { return; } // there wasn't a node here, abort
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for (;;) {
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leaders[who] = leader;
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if (who_ == who) { return; }
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who = who_;
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who_ = leaders[who];
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}
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}
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auto CountComponents(Grid const& grid) -> std::uint16_t {
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std::vector<std::uint16_t> leaders(128 * 128);
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// Visit all pairs of neighbors linking them if both are set
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for (std::uint16_t r = 0; r < 128; r++) {
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bool prev = false;
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for (std::uint16_t c = 0; c < 128; c++) {
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std::uint16_t me = r*128+c;
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// first time we've visited this node, if it's in the graph it's a leader!
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if (grid[r][c/8] & (1<<(7-(c%8)))) {
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leaders[me] = me;
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// If previous cell in row is a node, link it to me immediately
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// It will have just been set as its own group leader.
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if (prev) { leaders[me-1] = me; }
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// Connect up's leader _after_ updating left's leader in case they were connected
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if (0 < r) { Connect(leaders, me - 128, me); }
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prev = true;
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} else {
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prev = false;
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leaders[me] = -1;
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}
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}
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}
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// count component leaders
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std::uint16_t n = 0;
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for (std::size_t i = 0; i < leaders.size(); i++) {
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if (leaders[i] == i) { n++; }
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}
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return n;
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}
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} // namespace
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TEST_SUITE("2017-14 examples") {
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TEST_CASE("flqrgnkx") {
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auto rows = MakeRows("flqrgnkx");
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CHECK(CountBits(rows) == 8108);
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CHECK(CountComponents(rows) == 1242);
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}
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}
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auto main(int argc, char** argv) -> int {
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std::string input;
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std::getline(*aocpp::Startup(argc, argv), input);
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auto rows = MakeRows(std::move(input));
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std::cout << "Part 1: " << CountBits(rows) << std::endl;
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std::cout << "Part 2: " << CountComponents(rows) << std::endl;
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} |