Teaching and learning resources • Re: Advent of Code 2024

Code:

Advent of code 2024 day 6Part1 - 4982Part2 - 1663Elapsed time 20.6543 seconds

Code:

#include <iostream>#include <chrono>#include <fstream>#include <utility>#include <string>#include <vector>#include <map>const char* filename = "data.txt";using xy = std::pair<int,int>;xy operator +=(xy l,xy r){return {l.first + r.first,l.second + r.second};}// part 2 uses masksenum move{up = 0b1,right = 0b10,down = 0b100,left = 0b1000};xy next(xy c,move m){    switch(m)    {    case up: return c += {-1,0};    case right: return c += {0,1};    case down: return c += {1,0};    case left: return c += {0,-1};    }    return c;}move bump(move x){    switch(x)    {    case up: return right;    case right: return down;    case down: return left;    case left: break;    }    return up;}// pos is possible states of each position in the map// low bits are used by part 2enum pos{none = 0,done = 0xf0,block,off};bool test(xy start, std::map<int, std::vector<pos>>& map){    move face = up;    xy current = start;    while(true)    {        // current direction is face        xy newxy = next(current,face);        if(map[newxy.first][newxy.second] == block)            face = bump(face);        else            current = newxy;        pos& x = map[current.first][current.second];        if(x != off)        {            if(x & face)                return true;            else                x = static_cast<pos>(x | face);        }        else            break;    }    return false;}void clear(std::map<int ,std::vector<pos>>& map){    int height = map.size();    int width = map[0].size();    // clear all but obstacles and edges    for(int i = 1; i < height - 1; i++)        for(int j = 1; j < width - 1; j++)        {            if(map[i][j] != block)                map[i][j] = none;        }}int part2(xy start, std::map<int, std::vector<pos>>& map){    int height = map.size();    int width = map[0].size();    int count = 0;    for(int i = 1; i < height - 1; i++)    {        for(int j = 1; j < width - 1; j++)        {            if(map[i][j] != block && start != xy(i,j))            {                clear(map);                map[i][j] = block;                if(test(start,map))                    count++;                map[i][j] = none;            }        }    }    return count;}int part1(xy current, std::map<int, std::vector<pos>>& map){    int count = 0;    move face = up;    do    {        // process current position        if(map[current.first][current.second] != done)                count++;        map[current.first][current.second] = done;        // current direction is face        xy newxy = next(current,face);        if(map[newxy.first][newxy.second] == block)            face = bump(face);        else            current = newxy;    }while(map[current.first][current.second] != off);    return count;}int main(){    std::chrono::time_point<std::chrono::system_clock> start,stop;    start = std::chrono::system_clock::now();    std::cout << "Advent of code 2024 day 6" << "\n";    std::ifstream file(filename);    std::map<int, std::vector<pos>> map;    xy first;    if(file)    {        int x = 1;        std::string s;        std::getline(file,s);        int width = s.length() + 2;        std::vector<pos> line(width);        for(int i = 0; i < width ; i++)            line[i] = off;        map.emplace(0,line);        while(!file.eof())        {            line[0] = off;            for(int i  = 1; i < width - 1; i++)            {                if (s[i - 1] == '#')                    line[i] = block;                else                    line[i] = none;                if(s[i - 1] == '^')                    first = {x,i};            }               line[width - 1] = off;            map.emplace(x,line);             std::getline(file,s);            x++;        }        for(int i = 0; i < width ; i++)            line[i] = off;        map.emplace(x,line);    }    std::cout << "Part1 - " << part1(first,map) << "\n";    std::cout << "Part2 - " << part2(first,map) << "\n";    stop = std::chrono::system_clock::now();    std::chrono::duration<double> elapsed = stop - start;    std::cout << "Elapsed time " << elapsed.count() << " seconds" << "\n";    return 0;}