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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;

public class Main {
	final int _intMax = Integer.MAX_VALUE; // =2147483647>10^9
	final int _intMin = Integer.MIN_VALUE;
	final long _longMax = Long.MAX_VALUE; // =9223372036854775807L>10^18
	final long _longMin = Long.MIN_VALUE;
	final char[] _azAry = { 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r',
			's', 't', 'u', 'v', 'w', 'x', 'y', 'z' };

	void solve() {
		int[] ia = readNums();
		int h = ia[0];
		int w = ia[1];
		Bitmap map = new Bitmap(w, h);
		for (int y = 1; y <= h; y++) {
			String s = readLine();
			for (int x = 1; x <= w; x++) {
				if (s.charAt(x - 1) == '#')
					map.set(x, y, true);
			}
		}
		for (int y = 1; y <= h; y++) {
			for (int x = 1; x <= w; x++) {
				if (check(map, x, y)) {
					pln("No");
					return;
				}
			}
		}
		pln("Yes");
	}

	boolean check(Bitmap map, int x, int y) {
		if (!map.is(x, y))
			return false;
		if (map.is(x - 1, y))
			return false;
		if (map.is(x + 1, y))
			return false;
		if (map.is(x, y - 1))
			return false;
		if (map.is(x, y + 1))
			return false;
		return true;
	}

	// -----------------------------------------------------
	// 2018/05/05 r26
	// -----------------------------------------------------
	List<Character> getazList() {
		List<Character> list = new ArrayList<>();
		for (char ch : _azAry)
			list.add(ch);
		return list;
	}

	int getDx(int idx) {
		int[] dx = { 0, 1, 1, 1, 0, -1, -1, -1 };
		return dx[idx];
	}

	int getDy(int idx) {
		int[] dy = { -1, -1, 0, 1, 1, 1, 0, -1 };
		return dy[idx];
	}

	class Bitmap {
		int mx;
		int my;
		boolean[][] map;

		public Bitmap(int mx, int my) {
			this.mx = mx;
			this.my = my;
			map = new boolean[my + 2][mx + 2];
		}

		public boolean is(int x, int y) {
			return map[y][x];
		}

		public void set(int x, int y, boolean b) {
			map[y][x] = b;
		}
	}

	class CharList implements Iterable<Character> {
		class CharComparator implements Comparator<Character> {
			int sign;

			public CharComparator(boolean bAsc) {
				sign = bAsc ? 1 : -1;
			}

			public int compare(Character o1, Character o2) {
				return sign * Character.compare(o1, o2);
			}
		}

		List<Character> list = new ArrayList<>();
		CharComparator asc = new CharComparator(true);
		CharComparator desc = new CharComparator(false);

		public void add(char ch) {
			list.add(ch);
		}

		public char get(int idx) {
			return list.get(idx);
		}

		public char getLast() {
			return list.get(list.size() - 1);
		}

		public Iterator<Character> iterator() {
			return list.iterator();
		}

		public void remove(int idx) {
			list.remove(idx);
		}

		public void removeLast() {
			list.remove(list.size() - 1);
		}

		public int size() {
			return list.size();
		}

		public void sort(boolean bAsc) {
			if (bAsc)
				Collections.sort(list, asc);
			else
				Collections.sort(list, desc);
		}

		public String toString() {
			StringBuilder sb = new StringBuilder();
			for (char ch : list)
				sb.append(ch);
			return sb.toString();
		}
	}

	class Counter<K> {
		Map<K, Integer> map = new HashMap<>();

		public Counter() {
		}

		public Counter(Iterable<K> itr) {
			for (K obj : itr) {
				add(obj);
			}
		}

		public void add(K key) {
			Integer cnt = map.get(key);
			if (cnt == null)
				map.put(key, 1);
			else
				map.put(key, cnt + 1);
		}

		public int get(K key) {
			Integer cnt = map.get(key);
			if (cnt == null)
				return 0;
			else
				return cnt;
		}

		public Set<K> keySet() {
			return map.keySet();
		}
	}

	class IntList implements Iterable<Integer> {
		class Info {
			int idx;
			int val;

			public Info(int idx, int val) {
				this.idx = idx;
				this.val = val;
			}

			public String toString() {
				return "(" + idx + ", " + val + ")";
			}
		}

		class InfoComparator implements Comparator<Info> {
			int sign;

			public InfoComparator(boolean bAsc) {
				sign = bAsc ? 1 : -1;
			}

			public int compare(Info o1, Info o2) {
				return sign * Integer.compare(o1.val, o2.val);
			}
		}

		List<Info> list = new ArrayList<>();
		InfoComparator asc = new InfoComparator(true);
		InfoComparator desc = new InfoComparator(false);

		public IntList() {
		}

		public IntList(int[] ia) {
			for (int i = 0; i < ia.length; i++)
				add(ia[i]);
		}

		public void add(int val) {
			list.add(new Info(list.size(), val));
		}

		public void add(int idx, int val) {
			list.add(new Info(idx, val));
		}

		public int getIdx(int idx) {
			return list.get(idx).idx;
		}

		public int getVal(int idx) {
			return list.get(idx).val;
		}

		public int getLastVal() {
			return list.get(list.size() - 1).val;
		}

		public Iterator<Integer> iterator() {
			List<Integer> vallist = new ArrayList<>();
			for (Info info : list)
				vallist.add(info.val);
			return vallist.iterator();
		}

		public void remove(int idx) {
			list.remove(idx);
		}

		public void removeLast() {
			list.remove(list.size() - 1);
		}

		public int size() {
			return list.size();
		}

		public void sort(boolean bAsc) {
			if (bAsc)
				Collections.sort(list, asc);
			else
				Collections.sort(list, desc);
		}
	}

	class Point {
		int x;
		int y;

		public Point(int x, int y) {
			this.x = x;
			this.y = y;
		}

		public Point(Point pt) {
			this.x = pt.x;
			this.y = pt.y;
		}

		public boolean equals(Object o) {
			if (o instanceof Point) {
				Point that = (Point) o;
				return (x == that.x) && (y == that.y);
			}
			return false;
		}

		public long getManhattanDistance(Point pt) {
			return abs((long) pt.x - this.x) + abs((long) pt.y - this.y);
		}

		public int hashCode() {
			return x + (y * 31);
		}

		public String toString() {
			return "(" + x + ", " + y + ")";
		}
	}

	class PointList implements Iterable<Point> {
		class PointComparator implements Comparator<Point> {
			int mode;

			public PointComparator(int prop, boolean bAsc) {
				switch (prop) {
				case 1:
					if (bAsc)
						this.mode = 11;
					else
						this.mode = 12;
					break;
				case 2:
					if (bAsc)
						this.mode = 21;
					else
						this.mode = 22;
					break;
				default:
					throw new RuntimeException();
				}
			}

			public int compare(Point p1, Point p2) {
				switch (mode) {
				case 11:
					return 1 * Integer.compare(p1.x, p2.x);
				case 12:
					return -1 * Integer.compare(p1.x, p2.x);
				case 21:
					return 1 * Integer.compare(p1.y, p2.y);
				case 22:
					return -1 * Integer.compare(p1.y, p2.y);
				}
				throw new IllegalStateException();
			}
		}

		List<Point> list = new ArrayList<>();

		public void add(int x, int y) {
			list.add(new Point(x, y));
		}

		public Point get(int idx) {
			return list.get(idx);
		}

		public Iterator<Point> iterator() {
			return list.iterator();
		}

		public void remove(int idx) {
			list.remove(idx);
		}

		public int size() {
			return list.size();
		}

		public void sort(int prop, boolean bAsc) {
			PointComparator c = new PointComparator(prop, bAsc);
			Collections.sort(list, c);
		}
	}

	class StrList implements Iterable<String> {
		class StrComparator implements Comparator<String> {
			int sign;

			public StrComparator(boolean bAsc) {
				sign = bAsc ? 1 : -1;
			}

			public int compare(String o1, String o2) {
				return sign * o1.compareTo(o2);
			}
		}

		List<String> list = new ArrayList<>();
		StrComparator asc = new StrComparator(true);
		StrComparator desc = new StrComparator(false);

		public StrList() {
		}

		public StrList(String[] sa) {
			for (int i = 0; i < sa.length; i++)
				list.add(sa[i]);
		}

		public void add(String s) {
			list.add(s);
		}

		public String get(int idx) {
			return list.get(idx);
		}

		public Iterator<String> iterator() {
			return list.iterator();
		}

		public int size() {
			return list.size();
		}

		public void sort(boolean bAsc) {
			if (bAsc)
				Collections.sort(list, asc);
			else
				Collections.sort(list, desc);
		}
	}

	int abs(int a) {
		return (a >= 0) ? a : -a;
	}

	long abs(long a) {
		return (a >= 0) ? a : -a;
	}

	long ceil(long a, long b) {
		if (a < 0) {
			return -1 * floor(-a, b);
		}
		return ((a + b - 1) / b) * b;
	}

	long floor(long a, long b) {
		if (a < 0) {
			return -1 * ceil(-a, b);
		}
		return (a / b) * b;
	}

	int max(int a, int b) {
		return (a > b) ? a : b;
	}

	long max(long a, long b) {
		return (a > b) ? a : b;
	}

	int min(int a, int b) {
		return (a < b) ? a : b;
	}

	long min(long a, long b) {
		return (a < b) ? a : b;
	}

	int reed(long a, int n) {
		while (n-- > 0)
			a /= 10;
		return (int) (a % 10);
	}

	int sqrt(long a) {
		return (int) Math.sqrt(a);
	}

	int pint(String s) {
		return Integer.parseInt(s);
	}

	long plong(String s) {
		return Long.parseLong(s);
	}

	String readLine() {
		try {
			return _in.readLine();
		} catch (IOException e) {
			throw new RuntimeException(e);
		}
	}

	int readNum() {
		String line = readLine();
		return pint(line);
	}

	long readLong() {
		String line = readLine();
		return plong(line);
	}

	String[] readFlds() {
		String line = readLine();
		return line.split(" ");
	}

	String[] readLines(int n) {
		String[] lines = new String[n];
		for (int i = 0; i < n; i++)
			lines[i] = readLine();
		return lines;
	}

	CharList readChars() {
		CharList list = new CharList();
		String line = readLine();
		for (int i = 0; i < line.length(); i++)
			list.add(line.charAt(i));
		return list;
	}

	int[] readNums() {
		String[] flds = readFlds();
		int[] nums = new int[flds.length];
		for (int i = 0; i < flds.length; i++)
			nums[i] = pint(flds[i]);
		return nums;
	}

	int[] readNums(int n) {
		int[] nums = new int[n];
		for (int i = 0; i < n; i++)
			nums[i] = readNum();
		return nums;
	}

	long[] readLongs() {
		String[] flds = readFlds();
		long[] nums = new long[flds.length];
		for (int i = 0; i < flds.length; i++)
			nums[i] = plong(flds[i]);
		return nums;
	}

	long[] readLongs(int n) {
		long[] nums = new long[n];
		for (int i = 0; i < n; i++)
			nums[i] = readLong();
		return nums;
	}

	Main pln() {
		_out.println();
		return this;
	}

	Main p(char c) {
		_out.print(c);
		return this;
	}

	Main p(char c, int n) {
		for (int i = 0; i < n; i++)
			p(c);
		return this;
	}

	Main pln(char c) {
		_out.println(c);
		return this;
	}

	Main p(double d) {
		_out.print(d);
		return this;
	}

	Main pln(double d) {
		_out.println(d);
		return this;
	}

	Main p(long l) {
		_out.print(l);
		return this;
	}

	Main pln(long l) {
		_out.println(l);
		return this;
	}

	Main p(String s) {
		_out.print(s);
		return this;
	}

	Main p(String s, int idx) {
		_out.print(s.charAt(idx));
		return this;
	}

	Main pln(String s) {
		_out.println(s);
		return this;
	}

	Main pln(int[] ia) {
		for (int i = 0; i < ia.length; i++)
			_out.println(ia[i]);
		return this;
	}

	Main pln(long[] la) {
		for (int i = 0; i < la.length; i++)
			_out.println(la[i]);
		return this;
	}

	static BufferedReader _in;
	static PrintWriter _out;
	static boolean _bElapsed = false;

	public static void main(String[] args) {
		long start = System.currentTimeMillis();
		_in = new BufferedReader(new InputStreamReader(System.in));
		_out = new PrintWriter(System.out);
		new Main().solve();
		_out.flush();
		long end = System.currentTimeMillis();
		if (_bElapsed)
			System.err.println((end - start) + "ms");
	}
}