Thraix
94 lines
2.3 KiB
C++
94 lines
2.3 KiB
C++
#include "common/aoc.h"
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namespace y2024::day20
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{
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REGISTER_DAY(2024, Day20, Array2D<char>, int32_t);
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REGISTER_TEST_EXAMPLE(2024, Day20, ExampleInput, 1, 1);
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REGISTER_TEST(2024, Day20, Input, 1, 1429);
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REGISTER_TEST_EXAMPLE(2024, Day20, ExampleInput, 2, 285);
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REGISTER_TEST(2024, Day20, Input, 2, 988931);
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READ_INPUT(input)
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{
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return Input::ReadArray2D(input);
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}
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// Single path DFS, assumes the path can never hit a dead end
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static std::pair<int, std::vector<Index2D>> DFS(const Array2D<char>& map, const Index2D& initial)
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{
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std::vector<Index2D> path;
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Index2D prev = Index2D{-1, -1};
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std::pair<int, Index2D> cur{0, initial};
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path.emplace_back(initial);
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while (map[cur.second] != 'E')
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{
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for (auto dir : Helper::GetNeighborDirections())
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{
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Index2D pos = cur.second + dir;
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if (map.IsInside(pos))
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{
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if (pos != prev && map[pos] != '#')
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{
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prev = cur.second;
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cur.first++;
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cur.second = pos;
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path.emplace_back(pos);
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break;
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}
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}
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}
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}
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return {cur.first, path};
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}
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int Cheat(const Array2D<char>& map, int cheatTime, int diff)
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{
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int sum = 0;
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std::pair<int, std::vector<Index2D>> path = DFS(map, map.Find('S'));
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std::vector<int> distanceToGoal(map.width * map.height, -1);
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for (int i = 0; i < path.second.size(); i++)
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{
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distanceToGoal[map.GetIndex(path.second[i])] = path.second.size() - i - 1;
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}
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for (int i = 0; i < path.second.size(); i++)
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{
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for (int y = -cheatTime; y <= cheatTime; y++)
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{
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int yAbs = std::abs(y);
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for (int x = -cheatTime + yAbs; x <= cheatTime - yAbs; x++)
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{
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int xAbs = std::abs(x);
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int cost = i + xAbs + yAbs;
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Index2D pos{path.second[i].x + x, path.second[i].y + y};
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if (map.IsInside(pos))
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{
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int index = map.GetIndex(pos);
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if (distanceToGoal[index] >= 0)
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{
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if (cost + distanceToGoal[index] <= path.first - diff)
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{
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sum++;
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}
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}
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}
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}
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}
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}
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return sum;
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}
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OUTPUT1(input)
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{
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return Cheat(input, 2, isExample ? 50 : 100);
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}
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OUTPUT2(input)
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{
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return Cheat(input, 20, isExample ? 50 : 100);
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}
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}
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