AoC22/d12.cc

#include <iostream>
#include <vector>
#include <complex>
#include <deque>

//#define ANIMATE

using namespace std;

struct Input {
    vector<vector<unsigned char>> map;
    unsigned width;
    unsigned height;
    complex<int> start;
    complex<int> end;
};

complex<int> dirs[] = {
    complex<int>(1, 0),
    complex<int>(0, 1),
    complex<int>(-1, 0),
    complex<int>(0, -1)
};

Input parse()
{
    Input data;
    auto &map = data.map;
    for (string line; getline(cin, line);) {
        vector<unsigned char> row;
        for (auto x : line) {
            switch (x) {
            case 'S':
                data.start = complex<int>(row.size(), map.size());
                row.push_back('a' - 'a');
                break;
            case 'E':
                data.end = complex<int>(row.size(), map.size());
                row.push_back('z' - 'a');
                break;
            default: row.push_back(x - 'a'); break;
            }
        }
        data.map.push_back(row);
    }
    data.width = map.front().size();
    data.height = map.size();
    return data;
}

#ifdef ANIMATE
#include <fstream>
unsigned render_frame = 0;
void render(const Input &input, vector<vector<unsigned>> &dist, deque<complex<int>> &scan)
{
    auto scan_map = (bool (*)[input.width])new bool[input.width * input.height]();
    for (auto &x : scan) {
        scan_map[x.imag()][x.real()] = true;
    }

    char fname[] = "img/00000.pam";
    sprintf(fname, "img/%05u.pam", render_frame++);
    auto file = ofstream(fname);
    file << "P7\n";
    file << "WIDTH " << input.width << '\n';
    file << "HEIGHT " << input.height << '\n';
    file << "DEPTH 3\nMAXVAL 255\nTUPLTYPE RGB\nENDHDR\n";

    unsigned maxdist = 0;
    for (unsigned y = 0; y < input.height; y++) {
        for (unsigned x = 0; x < input.width; x++) {
            unsigned d = dist[y][x];
            if (d > maxdist) maxdist = d;
        }
    }

    for (unsigned y = 0; y < input.height; y++) {
        for (unsigned x = 0; x < input.width; x++) {
            uint32_t color = 0;
            color |= ((dist[y][x] * 0xFF / maxdist) & 0xFF) << 8;
            color |= input.map[y][x] * 0xFF / 26;
            if (scan_map[y][x]) color = 0xFF0000;
            file.write((char *)&color, 3);
        }
    }
    file.close();
    delete scan_map;
}
#endif

vector<vector<unsigned>> calc_dist(const Input &input)
{
    vector<vector<unsigned>> dist(input.height, vector<unsigned>(input.width));
    auto &map = input.map;

    deque<complex<int>> scan;
    scan.push_back(input.end);
    dist[input.end.imag()][input.end.real()] = 1;

    while (!scan.empty()) {
        auto pos = scan.front();
        unsigned pos_d = dist[pos.imag()][pos.real()];
        unsigned pos_h = map[pos.imag()][pos.real()];
        scan.pop_front();

        for (auto dir : dirs) {
            auto newpos = pos + dir;

            // Make sure the new position is in-bounds
            if (newpos.imag() < 0 || newpos.imag() >= (int)input.height) continue;
            if (newpos.real() < 0 || newpos.real() >= (int)input.width) continue;

            // If the distance for this position has already been calculated,
            //  and is smaller than the current pos' distance, skip it.
            unsigned &newpos_d = dist[newpos.imag()][newpos.real()];
            if (newpos_d && newpos_d <= pos_d + 1) continue;

            // Make sure the height difference isn't too big
            unsigned newpos_h = map[newpos.imag()][newpos.real()];
            if ((int)pos_h - (int)newpos_h > 1) continue;

            // Otherwise, continue down this path
            newpos_d = pos_d + 1;
            scan.push_back(newpos);
        }
#ifdef ANIMATE
        render(input, dist, scan);
#endif
    }
    return dist;
}

unsigned p1(const Input &input, const vector<vector<unsigned>> &dist)
{
    unsigned end_dist = dist[input.start.imag()][input.start.real()];
    if (end_dist) end_dist--;
    return end_dist;
}

unsigned p2(const Input &input, const vector<vector<unsigned>> &dist)
{
    unsigned smallest = dist[input.start.imag()][input.start.real()];
    for (unsigned y = 0; y < input.height; y++) {
        for (unsigned x = 0; x < input.width; x++) {
            if (input.map[y][x] == 0) {
                unsigned d = dist[y][x];
                if (d && d < smallest) smallest = d;
            }
        }
    }
    if (smallest) smallest--;
    return smallest;
}

int main()
{
    auto input = parse();
    auto dist = calc_dist(input);
    cout << p1(input, dist) << endl;
    cout << p2(input, dist) << endl;
}