using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var data = new int [5, 5] {

            { 1, 0, 0, 1, 0 },

            { 1, 0, 1, 0, 0 },

            { 0, 0, 1, 0, 1 },

            { 1, 0, 1, 0, 1 },

            { 1, 0, 1, 1, 0 }

        };

        //Console.WriteLine(string.Format("{0}, {1}", data.GetUpperBound(0), data.GetUpperBound(1)));

        var solution = new Solution();

        var answers = solution.GetRiverSizes(data);

        foreach (var answer in answers)

        {

            Console.Write(string.Format("{0}, ", answer));

        }

    }

}

​

public class Solution

{

    public int[] GetRiverSizes(int[,] matrix) 

    {

        var riverSizes = new List<int>();

        var visited = new bool[matrix.GetUpperBound(0) + 1, matrix.GetUpperBound(1) + 1];

​

        //BFSHelper(1, 2, matrix, visited, riverSizes);

        for (var i = 0; i <= matrix.GetUpperBound(0); i++) 

        {

            for (var j = 0; j <= matrix.GetUpperBound(1); j++) 

            {

                if (!visited[i, j]) 

                {

                    BFSHelper(i, j, matrix, visited, riverSizes);

                }

            }

        }

        return riverSizes.ToArray();

    }

    public void BFSHelper(int startRow, int startCol, int[,] matrix, bool[,] visited, List<int> riverSizes) {

        var riverSize = 0;

        var queue = new Queue<Node>();

        queue.Enqueue(new Node { rowIndex = startRow, colIndex = startCol });

        while (queue.Count > 0)

        {

            var current = queue.Dequeue();

            //Console.WriteLine(string.Format("[{0}][{1}] = {2} : {3}", current.rowIndex, current.colIndex, matrix[current.rowIndex, current.colIndex], visited[current.rowIndex, current.colIndex] ));

            if (!visited[current.rowIndex, current.colIndex]) 

            {

                visited[current.rowIndex, current.colIndex] = true;

​

                if (matrix[current.rowIndex, current.colIndex] == 1)

                {

                    //Console.WriteLine(string.Format("[{0}][{1}] = {2} : {3}", current.rowIndex, current.colIndex, matrix[current.rowIndex, current.colIndex], visited[current.rowIndex, current.colIndex] ));

                    riverSize++;

                    if (current.rowIndex - 1 >= 0)

                    {

                        queue.Enqueue(new Node { rowIndex = current.rowIndex - 1, colIndex = current.colIndex });

                        //Console.WriteLine(string.Format("\tA[{0}][{1}] = {2} : {3}", current.rowIndex - 1, current.colIndex, matrix[current.rowIndex - 1, current.colIndex], visited[current.rowIndex - 1, current.colIndex] ));

                    }

                    if (current.colIndex + 1 <= matrix.GetUpperBound(1))

                    {

                        queue.Enqueue(new Node { rowIndex = current.rowIndex, colIndex = current.colIndex + 1 });

                        //Console.WriteLine(string.Format("\tB[{0}][{1}] = {2} : {3}", current.rowIndex, current.colIndex + 1, matrix[current.rowIndex, current.colIndex + 1], visited[current.rowIndex, current.colIndex + 1] ));

                    }

                    if (current.rowIndex + 1 <= matrix.GetUpperBound(0))

                    {

                        queue.Enqueue(new Node { rowIndex = current.rowIndex + 1, colIndex = current.colIndex });

                        //Console.WriteLine(string.Format("\tC[{0}][{1}] = {2} : {3}", current.rowIndex + 1, current.colIndex, matrix[current.rowIndex + 1, current.colIndex], visited[current.rowIndex + 1, current.colIndex] ));

                    }

                    if (current.colIndex - 1 >= 0){

                        queue.Enqueue(new Node { rowIndex = current.rowIndex, colIndex = current.colIndex - 1 });

                        //Console.WriteLine(string.Format("\tD[{0}][{1}] = {2} : {3}", current.rowIndex, current.colIndex - 1, matrix[current.rowIndex, current.colIndex - 1], visited[current.rowIndex, current.colIndex - 1] ));

                    }

                }

            }

        }

        if (riverSize > 0) riverSizes.Add(riverSize);

    }

}

​

public class Node {

    public int rowIndex { get; set; }

    public int colIndex { get; set; }

}