Advent of Code 2020 - Day 11 Seating System

day11_seating_system.cpp

#include <algorithm>
#include <fstream>
#include <iostream>
#include <string>
#include <vector>

using namespace std;

#define forn(i, j, n) for (int i = j; i < (int)n; i++)
#define forr(i, j, n) for (int i = j; i >= (int)n; i--)
#define fore(i, coll) for (auto i : coll)
#define endl '\n'
#define pb push_back
#define all(x) x.begin(), x.end()

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<string> vs;

int count_occupied_adjacent(vs &, int, int);
int count_occupied_visible(vs &, int, int);
pii predict_seats(vs &, int, int(vs &, int, int));

const char OCCUPIED = '#';
const char FREE = 'L';
const char FLOOR = '.';

int main() {
    ifstream fin("inputs/11.txt");

    int changes_count, seats_occupied;
    vs part1_area, part2_area;

    // inputs read (one copy for each problem part)
    string line;
    while (fin >> line) {
        part1_area.pb(line);
        part2_area.pb(line);
    }

    // part 1
    while (true) {
        pii values = predict_seats(part1_area, 4, count_occupied_adjacent);
        seats_occupied = values.first;
        changes_count = values.second;
        if (changes_count == 0) break;
    }
    cout << "Part 1: " << seats_occupied << endl;

    // part 2
    while (true) {
        pii values = predict_seats(part2_area, 5, count_occupied_visible);
        seats_occupied = values.first;
        changes_count = values.second;
        if (changes_count == 0) break;
    }
    cout << "Part 2: " << seats_occupied << endl;

    return 0;
}

pii predict_seats(vs &area, int tolerance, int validator(vs &, int, int)) {
    int seats_occupied = 0, changes_count = 0;
    vs grid;
    for (auto row : area) grid.pb(row);

    forn(row, 0, area.size()) {
        forn(col, 0, area[0].size()) {
            char seat = area[row][col];
            if (area[row][col] != FLOOR) {
                int occupied = validator(grid, row, col);
                if (area[row][col] == FREE and occupied == 0) seat = OCCUPIED;
                if (area[row][col] == OCCUPIED and occupied >= tolerance) seat = FREE;
                changes_count += area[row][col] != seat;
                if (seat == OCCUPIED) seats_occupied++;
            }
            area[row][col] = seat;
        }
    }
    return {seats_occupied, changes_count};
}

// part 1 validator, search for occupied adjacent seats
int count_occupied_adjacent(vs &grid, int r, int c) {
    int cnt = 0, rows = grid.size(), cols = grid[0].size();
    // seats above
    if (r - 1 >= 0 && c - 1 >= 0 && grid[r - 1][c - 1] == OCCUPIED) cnt++;
    if (r - 1 >= 0 && grid[r - 1][c] == OCCUPIED) cnt++;
    if (r - 1 >= 0 && c + 1 < cols && grid[r - 1][c + 1] == OCCUPIED) cnt++;

    // seats on the sides
    if (c - 1 >= 0 && grid[r][c - 1] == OCCUPIED) cnt++;
    if (c + 1 < cols && grid[r][c + 1] == OCCUPIED) cnt++;

    // seats below
    if (r + 1 < rows && c - 1 >= 0 && grid[r + 1][c - 1] == OCCUPIED) cnt++;
    if (r + 1 < rows && grid[r + 1][c] == OCCUPIED) cnt++;
    if (r + 1 < rows && c + 1 < cols && grid[r + 1][c + 1] == '#') cnt++;
    return cnt;
}

// part 2 validator , search for occupied visible seats
int count_occupied_visible(vs &grid, int row, int col) {
    int cnt = 0, rows = grid.size(), cols = grid[0].size();
    bool occupied;

    occupied = false;  // north
    forr(i, row - 1, 0) {
        if (grid[i][col] == OCCUPIED) occupied = true;
        if (grid[i][col] == FREE) break;
    }
    cnt += occupied;

    occupied = false;  // south
    forn(i, row + 1, rows) {
        if (grid[i][col] == OCCUPIED) occupied = true;
        if (grid[i][col] == FREE) break;
    }
    cnt += occupied;

    occupied = false;  // west (left)
    forr(i, col - 1, 0) {
        if (grid[row][i] == OCCUPIED) occupied = true;
        if (grid[row][i] == FREE) break;
    }
    cnt += occupied;

    occupied = false;  // east (right)
    forn(i, col + 1, cols) {
        if (grid[row][i] == OCCUPIED) occupied = true;
        if (grid[row][i] == FREE) break;
    }
    cnt += occupied;

    occupied = false;  // north west (diag1)
    for (int i = row - 1, j = col - 1; i >= 0 && j >= 0; i--, j--) {
        if (grid[i][j] == OCCUPIED) occupied = true;
        if (grid[i][j] == FREE) break;
    }
    cnt += occupied;

    occupied = false;  // south east (diag1)
    for (int i = row + 1, j = col + 1; i < rows && j < cols; i++, j++) {
        if (grid[i][j] == OCCUPIED) occupied = true;
        if (grid[i][j] == FREE) break;
    }
    cnt += occupied;

    occupied = false;  // north east (diag2)
    for (int i = row - 1, j = col + 1; i >= 0 && j < cols; i--, j++) {
        if (grid[i][j] == OCCUPIED) occupied = true;
        if (grid[i][j] == FREE) break;
    }
    cnt += occupied;

    occupied = false;  // south west (diag2)
    for (int i = row + 1, j = col - 1; i < rows && j >= 0; i++, j--) {
        if (grid[i][j] == OCCUPIED) occupied = true;
        if (grid[i][j] == FREE) break;
    }
    cnt += occupied;
    return cnt;
}