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.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using static kyoupuro.Input;
using static kyoupuro.MyMath;
using static kyoupuro.Modular;

namespace kyoupuro {

    class MainClass {

        public static void Main() {
            int h = NextInt, w = NextInt;
            var list = new List<string>();

            for (int i = 0; i < h; i++) {
                list.Add(Line);
            }

            for (int i = 0; i < h; i++) {
                for (int j = 0; j < w; j++) {
                    if (list[i][j] == '#') {
                        bool ok = false;
                        if (i > 0) ok |= list[i - 1][j] == '#';
                        if (j > 0) ok |= list[i][j - 1] == '#';
                        if (i + 1 < h) ok |= list[i + 1][j] == '#';
                        if (j + 1 < w) ok |= list[i][j + 1] == '#';

                        if(!ok) {
                            Console.WriteLine("No");
                            return;
                        }
                    }
                }
            }

            Console.WriteLine("Yes");
        }
    }

    class MyMath {
        public static long Gcd(long a, long b) {
            return b == 0 ? a : Gcd(b, a % b);
        }

        public static long Sqrt(long n) {
            if (n < 0) return 0;
            long a = 0, tmp = 0, b = 0;
            for (int i = 62; i >= 0; i -= 2) {
                tmp = (b << 1) + 1 <= (n >> i) ? 1 : 0;
                a = a << 1 | tmp;
                n -= (((b << 1) + 1) * tmp) << i;
                b = (b << 1) + tmp + tmp;
            }
            return a;
        }

        public static long Nck(int n, int k) {
            if (k == 0) return 1;
            if (n == 0) return 0;
            return n * Nck(n - 1, k - 1) / k;
        }
    }

    class Modular {
        public const int mod = 1000000007;
        public readonly long value;
        public Modular(long value) { this.value = value; }
        public static implicit operator Modular(long a) {
            var m = a % mod;
            return new Modular((m < 0) ? m + mod : m);
        }
        public static Modular operator +(Modular a, Modular b) {
            return a.value + b.value;
        }
        public static Modular operator -(Modular a, Modular b) {
            return a.value - b.value;
        }
        public static Modular operator *(Modular a, Modular b) {
            return a.value * b.value;
        }
        private static Modular Pow(Modular a, int n) {
            switch (n) {
                case 0:
                    return 1;
                case 1:
                    return a;
                default:
                    var p = Pow(a, n / 2);
                    return p * p * Pow(a, n % 2);
            }
        }
        public static Modular operator /(Modular a, Modular b) {
            return a * Pow(b, mod - 2);
        }
        private static readonly List<int> facs = new List<int> { 1 };
        private static Modular Fac(int n) {
            for (int i = facs.Count; i <= n; ++i) {
                facs.Add((int)(Math.BigMul(facs.Last(), i) % mod));
            }
            return facs[n];
        }
        public static Modular Ncr(int n, int r) {
            return (n < r) ? 0
                 : (n == r) ? 1
                            : Fac(n) / (Fac(r) * Fac(n - r));
        }
        public static explicit operator int(Modular a) {
            return (int)a.value;
        }
    }

    public class PriorityQueue<T> {

        readonly List<T> _heap = new List<T>();
        readonly Comparison<T> _comparison;

        public PriorityQueue(Comparison<T> comparison) {
            _comparison = comparison;
        }

        public PriorityQueue() : this(Comparer<T>.Default.Compare) { }

        public PriorityQueue(IComparer<T> comparer) : this(comparer.Compare) { }

        public void Enqueue(T item) {
            _heap.Add(item);

            int childID = _heap.Count - 1;
            int parentID = (childID - 1) / 2;

            while (childID > 0 && _comparison(_heap[parentID], _heap[childID]) > 0) {
                Swap(parentID, childID);
                childID = parentID;
                parentID = (parentID - 1) / 2;
            }
        }

        public T Dequeue() {
            var first = _heap.First();
            _heap[0] = _heap.Last();
            _heap.RemoveAt(_heap.Count - 1);

            int parentID = 0;
            int childID = parentID * 2 + 2;
            if (childID >= _heap.Count || _comparison(_heap[childID], _heap[childID - 1]) > 0) childID--;

            while (childID < _heap.Count && _comparison(_heap[parentID], _heap[childID]) > 0) {
                Swap(parentID, childID);
                parentID = childID;
                childID = parentID * 2 + 2;
                if (childID >= _heap.Count || _comparison(_heap[childID], _heap[childID - 1]) > 0) childID--;
            }

            return first;
        }

        void Swap(int parent, int child) {
            var tmp = _heap[parent];
            _heap[parent] = _heap[child];
            _heap[child] = tmp;
        }

        public T Peek() { return _heap[0]; }
        public int Count => _heap.Count;
        public bool Any() { return _heap.Any(); }
        public List<T> Data => _heap;
    }

    public class UnionFind {
        public int[] Parents { get; set; }
        public UnionFind(int size) {
            Parents = Enumerable.Repeat(-1, size).ToArray();
        }

        public int Find(int num) {
            if (Parents[num] < 0) return num;

            Parents[num] = Find(Parents[num]);
            return Parents[num];
        }

        public int Size(int num) {
            return -Parents[Find(num)];
        }

        public bool Same(int a, int b) {
            return Find(a) == Find(b);
        }

        public void Unite(int a, int b) {
            int x = Find(a), y = Find(b);

            if (Size(x) > Size(y)) {
                Parents[x] += Parents[y];
                Parents[y] = x;
            } else {
                Parents[y] += Parents[x];
                Parents[x] = y;
            }
        }
    }

    class Input {
        static IEnumerator<string> enumerator = new string[] { }.AsEnumerable().GetEnumerator();

        public static string Line => Console.ReadLine();

        public static string[] StrArr => Line.Split(' ');

        public static int NextInt => int.Parse(NextWord());

        public static long NextLong => long.Parse(NextWord());

        public static List<int> IntList => StrArr.Select(int.Parse).ToList();

        public static List<long> LongList => StrArr.Select(long.Parse).ToList();

        public static string NextWord() {
            while (!enumerator.MoveNext()) {
                enumerator = StrArr.AsEnumerable().GetEnumerator();
            }
            return enumerator.Current;
        }
    }
}