Problem:
Score: 300 points

Problem Statement

We have a canvas divided into a grid with H rows and W columns. The square at the i-th row from the top and the j-th column from the left is represented as (i, j).

Initially, all the squares are white. square1001 wants to draw a picture with black paint. His specific objective is to make Square (i, j) black when s_{i, j}= #, and to make Square (i, j) white when s_{i, j}= ..

However, since he is not a good painter, he can only choose two squares that are horizontally or vertically adjacent and paint those squares black, for some number of times (possibly zero). He may choose squares that are already painted black, in which case the color of those squares remain black.

Determine if square1001 can achieve his objective.

Constraints

H is an integer between 1 and 50 (inclusive).

W is an integer between 1 and 50 (inclusive).

For every (i, j) (1 \leq i \leq H, 1 \leq j \leq W), s_{i, j} is # or ..

Input

Input is given from Standard Input in the following format:

H W
s_{1, 1} s_{1, 2} s_{1, 3} ... s_{1, W}
s_{2, 1} s_{2, 2} s_{2, 3} ... s_{2, W}
: :
s_{H, 1} s_{H, 2} s_{H, 3} ... s_{H, W}

Output

If square1001 can achieve his objective, print Yes; if he cannot, print No.

Sample Input 1

3 3
.#.
###
.#.

Sample Output 1

Yes

One possible way to achieve the objective is shown in the figure below. Here, the squares being painted are marked by stars.

Sample Input 2

5 5
#.#.#
.#.#.
#.#.#
.#.#.
#.#.#

Sample Output 2

No

square1001 cannot achieve his objective here.

Sample Input 3

11 11
...#####...
.##.....##.
#..##.##..#
#..##.##..#
#.........#
#...###...#
.#########.
.#.#.#.#.#.
##.#.#.#.##
..##.#.##..
.##..#..##.

Sample Output 3

Yes

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Text;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
using static System.Math;

namespace AtCoder
{
    public class Program
    {
        public static void Main(string[] args)
        {
            new Program().Solve(new ConsoleInput(Console.In, ' '));
            System.Threading.Thread.Sleep(1000);
        }

        public void Solve(ConsoleInput cin)
        {
            int h = cin.ReadInt;
            int w = cin.ReadInt;

            string[,] map = new string[h, w];
            for (int i = 0; i < h; i++)
            {
                char[] l = cin.ReadLine.ToCharArray();
                for (int j = 0; j < w; j++)
                {
                    map[i, j] = l[j].ToString();
                }
            }

            bool can = true;
            for (int i = 0; i < h; i++)
                for (int j = 0; j < w; j++)
                {
                    if (map[i, j].Equals(".")) continue;
                    if (i > 0 && map[i - 1, j].Equals("#")) continue;
                    if (j > 0 && map[i, j - 1].Equals("#")) continue;
                    if (i < h-1 && map[i + 1, j].Equals("#")) continue;
                    if (j < w-1 && map[i, j + 1].Equals("#")) continue;
                    can = false;
                }

            Console.WriteLine(can ? "Yes" : "No");
        }
    }

    public class ConsoleInput
    {
        private readonly System.IO.TextReader _stream;
        private char _separator = ' ';
        private Queue<string> inputStream;
        public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
        {
            this._separator = separator;
            this._stream = stream;
            inputStream = new Queue<string>();
        }
        public string Read
        {
            get
            {
                if (inputStream.Count != 0) return inputStream.Dequeue();
                string[] tmp = _stream.ReadLine().Split(_separator);
                for (int i = 0; i < tmp.Length; ++i)
                    inputStream.Enqueue(tmp[i]);
                return inputStream.Dequeue();
            }
        }
        public string ReadLine { get { return _stream.ReadLine(); } }
        public int ReadInt { get { return int.Parse(Read); } }
        public long ReadLong { get { return long.Parse(Read); } }
        public double ReadDouble { get { return double.Parse(Read); } }
        public string[] ReadStrArray(long num) { var ret = new string[num]; for (long i = 0; i < num; ++i) ret[i] = Read; return ret; }
        public int[] ReadIntArray(long num) { var ret = new int[num]; for (long i = 0; i < num; ++i) ret[i] = ReadInt; return ret; }
        public long[] ReadLongArray(long num) { var ret = new long[num]; for (long i = 0; i < num; ++i) ret[i] = ReadLong; return ret; }
    }
}