Medium Google Coding Interview With Ben Awad

using System.Numerics;

int[,] matrix = {
    { 1, 0, 0, 0, 0, 0 },
    { 0, 1, 0, 1, 1, 1 },
    { 0, 0, 1, 0, 1, 0 },
    { 1, 1, 0, 0, 1, 0 },
    { 1, 0, 1, 1, 0, 0 },
    { 1, 0, 0, 0, 0, 1 },
};

void Print(int[,] matrix)
{
    for (int i = 0; i < matrix.GetLength(0); i++)
    {
        for (int j = 0; j < matrix.GetLength(1); j++)
        {
            Console.Write(matrix[i, j] + ",");
        }
        Console.WriteLine();
    }
}

// b
var linkBorder = new bool[matrix.GetLength(0), matrix.GetLength(1)];

// todo: explore this
// var m = new Matrix3x2();

static void RemoveIslands(int[,] matrix, bool[,] borderLink)
{
    // int[,] directions = {
    //     { 0, -1 }, // left
    //     { 0, 1 }, // right
    //     { 1, 0 }, // down
    //     { -1, 0 }, // up
    // };

    (int, int)[] directions = {
        (0, -1), // left
        (0, 1), // right
        (1, 0), // down
        (-1, 0), // up
    };

    var rowCount = matrix.GetLength(0);
    var colCount = matrix.GetLength(1);
    for (int r = 0; r < rowCount; r++)
    {
        for (int c = 0; c < colCount; c++)
        {
            if (matrix[r, c] == 1 && IsOneBorderAdjacent(r, c, rowCount, colCount) == borderLink[r, c] == false)
            {
                borderLink[r, c] = true;
                CheckNeighbors(r, c);
            }
        }
    }

    for (int i = 0; i < borderLink.GetLength(0); i++)
    {
        for (int j = 0; j < borderLink.GetLength(1); j++)
        {
            if (borderLink[i, j] == false)
            {
                matrix[i, j] = 0;
            }
        }
    }

    void CheckNeighbors(int r, int c)
    {
        foreach ((int row, int col) direction in directions)
        {
            int nextRow = r + direction.row;
            int nextCol = c + direction.col;
            // invalid direction
            if (!IsWithinPerimeter(nextRow, nextCol, rowCount, colCount) || matrix[nextRow, nextCol] != 1)
            {
                continue;
            }
            if (matrix[nextRow, nextCol] == 1 && borderLink[nextRow, nextCol] == false)
            {
                borderLink[nextRow, nextCol] = true;
                CheckNeighbors(nextRow, nextCol);
            }
        }
    }
}

// for a fized
static bool IsOneBorderAdjacent(int row, int col, int rowCount, int colCount)
{
    if (!IsWithinPerimeter(row, col, rowCount, colCount)) return false;
    return (row == 0 || row + 1 == rowCount || col + 1 == colCount);
}

// validates if the coords are within bound to not go outside of perimeter of the matrix
static bool IsWithinPerimeter(int row, int col, int rowCount, int colCount)
{
    return row >= 0 && row < rowCount && col >= 0 && col < colCount;
}

static void Analyzes(int[,] matrix)
{
    foreach (int value in new[,] { { 1, 2 }, { 3, 4 } })
    {
        // output: 1,2,3,4
        Console.WriteLine(value);
    }

    Console.WriteLine(matrix.Length);
    Console.WriteLine(matrix.GetLength(0));
    Console.WriteLine(matrix.GetLength(1));
}

Print(matrix);
// Analyzes(matrix);
RemoveIslands(matrix, linkBorder);
Console.WriteLine("=========================");
Print(matrix);

// Inspired from: https://www.youtube.com/watch?v=4tYoVx0QoN0&t=2518s