AOC2024 Problem 4 Part 2

aoc-2024-4-2.cpp

#include <iostream>
#include <fstream>
#include <string>
#include <ctype.h>
#include <vector>
#include <algorithm>
#include <unordered_map>
#include <sstream>
#include <regex>

using namespace std;

bool checkConstraints(int row, int col, int rows, int cols) {
    if (row < 0 || row >= rows || col < 0 || col >= cols) {
        return false;
    }
    return true;
}

// Helper to check if "XMAS" exists starting at (row, col) in the given direction
bool isXMASInDirection(const std::vector<std::string>& grid, int row, int col) {
    if (grid[row][col] != 'A') {
        return false; // In the center of MAS cross is the 'A'
    }
    int rows = grid.size();
    int cols = grid[0].size();

    // Check the top to bottom diagonal
    int topLeftRow = row - 1;
    int topLeftCol = col - 1;
    if (!checkConstraints(topLeftRow, topLeftCol, rows, cols)) {
        return false;
    }
    int bottomRightRow = row + 1;
    int bottomRightCol = col + 1;
    if (!checkConstraints(bottomRightRow, bottomRightCol, rows, cols)) {
        return false;
    }

    bool topToBottom = false;

    // Maybe we have MAS spelled from top to bottom or reverse?
    if ((grid[topLeftRow][topLeftCol] == 'M' &&
        grid[bottomRightRow][bottomRightCol] == 'S') ||
        (grid[topLeftRow][topLeftCol] == 'S' &&
            grid[bottomRightRow][bottomRightCol] == 'M')) {
        topToBottom = true;
    }

    // Check the bottom to top diagonal /
    int bottomLeftRow = row + 1;
    int bottomLeftCol = col - 1;

    if (!checkConstraints(bottomLeftRow, bottomLeftCol, rows, cols)) {
        return false;
    }

    int topRightRow = row - 1;
    int topRightCol = col + 1;
    if (!checkConstraints(topRightRow, topRightCol, rows, cols)) {
        return false;
    }

    // Maybe we have MAS spelled from top to bottom or reverse?
    if ((grid[bottomLeftRow][bottomLeftCol] == 'M' &&
        grid[topRightRow][topRightCol] == 'S') ||
        (grid[bottomLeftRow][bottomLeftCol] == 'S' &&
            grid[topRightRow][topRightCol] == 'M')) {
        if (topToBottom) {
            return true;
        }
    }

    return false;
}

// Count all occurrences of "XMAS" in all directions
int countXMASOccurrences(const std::vector<std::string>& grid) {
    int count = 0;
    int rows = grid.size();
    int cols = grid[0].size();

    for (int row = 0; row < rows; ++row) {
        for (int col = 0; col < cols; ++col) {
            if (isXMASInDirection(grid, row, col)) {
                ++count;
            }
        }
    }

    return count;
}


int main()
{
    ifstream infile("input.txt");

    if (!infile.is_open()) {
        cout << "File prob\n";
        return -1;
    }
    string line;
    std::vector<std::string> grid;
    while (infile.good()) {
        getline(infile, line);
        if (line.empty()) continue;

        
        grid.push_back(line);
    }

    int count = countXMASOccurrences(grid);

    std::cout << count << std::endl;
}