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 Go (1.6) (judge verdict: Accepted)

package main

import (
	"bufio"
	"errors"
	"fmt"
	"math"
	"os"
	"strconv"
	"strings"
)

/*
var rdr = bufio.NewReaderSize(os.Stdin, 1000000)
// readLine can read long line string (at least 10^5)
func readLine() string {
	buf := make([]byte, 0, 1000000)
	for {
		l, p, e := rdr.ReadLine()
		if e != nil {
			panic(e)
		}
		buf = append(buf, l...)
		if !p {
			break
		}
	}
	return string(buf)
}
// NextLine reads a line text from stdin, and then returns its string.
func NextLine() string {
	return readLine()
}
*/

var sc = bufio.NewScanner(os.Stdin)

// NextLine reads a line text from stdin, and then returns its string.
func NextLine() string {
	sc.Scan()
	return sc.Text()
}

// NextIntsLine reads a line text, that consists of **ONLY INTEGERS DELIMITED BY SPACES**, from stdin.
// And then returns intergers slice.
func NextIntsLine() []int {
	ints := []int{}
	intsStr := NextLine()
	tmp := strings.Split(intsStr, " ")
	for _, s := range tmp {
		integer, _ := strconv.Atoi(s)
		ints = append(ints, integer)
	}
	return ints
}

// NextStringsLine reads a line text, that consists of **STRINGS DELIMITED BY SPACES**, from stdin.
// And then returns strings slice.
func NextStringsLine() []string {
	str := NextLine()
	return strings.Split(str, " ")
}

// NextRunesLine reads a line text, that consists of **ONLY CHARACTERS ARRANGED CONTINUOUSLY**, from stdin.
// Ant then returns runes slice.
func NextRunesLine() []rune {
	return []rune(NextLine())
}

// Max returns the max integer among input set.
// This function needs at least 1 argument (no argument causes panic).
func Max(integers ...int) int {
	m := integers[0]
	for i, integer := range integers {
		if i == 0 {
			continue
		}
		if m < integer {
			m = integer
		}
	}
	return m
}

// Min returns the min integer among input set.
// This function needs at least 1 argument (no argument causes panic).
func Min(integers ...int) int {
	m := integers[0]
	for i, integer := range integers {
		if i == 0 {
			continue
		}
		if m > integer {
			m = integer
		}
	}
	return m
}

// PowInt is integer version of math.Pow
func PowInt(a, e int) int {
	if a < 0 || e < 0 {
		panic(errors.New("[argument error]: PowInt does not accept negative integers"))
	}
	fa := float64(a)
	fe := float64(e)
	fanswer := math.Pow(fa, fe)
	return int(fanswer)
}

// AbsInt is integer version of math.Abs
func AbsInt(a int) int {
	fa := float64(a)
	fanswer := math.Abs(fa)
	return int(fanswer)
}

// DeleteElement returns a *NEW* slice, that have the same and minimum length and capacity.
// DeleteElement makes a new slice by using easy slice literal.
func DeleteElement(s []int, i int) []int {
	if i < 0 || len(s) <= i {
		panic(errors.New("[index error]"))
	}
	// appendのみの実装
	n := make([]int, 0, len(s)-1)
	n = append(n, s[:i]...)
	n = append(n, s[i+1:]...)
	return n
}

// Concat returns a *NEW* slice, that have the same and minimum length and capacity.
func Concat(s, t []rune) []rune {
	n := make([]rune, 0, len(s)+len(t))
	n = append(n, s...)
	n = append(n, t...)
	return n
}

// UpperRune is rune version of `strings.ToUpper()`.
func UpperRune(r rune) rune {
	str := strings.ToUpper(string(r))
	return []rune(str)[0]
}

// LowerRune is rune version of `strings.ToLower()`.
func LowerRune(r rune) rune {
	str := strings.ToLower(string(r))
	return []rune(str)[0]
}

// ToggleRune returns a upper case if an input is a lower case, v.v.
func ToggleRune(r rune) rune {
	var str string
	if 'a' <= r && r <= 'z' {
		str = strings.ToUpper(string(r))
	} else if 'A' <= r && r <= 'Z' {
		str = strings.ToLower(string(r))
	} else {
		str = string(r)
	}
	return []rune(str)[0]
}

// ToggleString iteratively calls ToggleRune, and returns the toggled string.
func ToggleString(s string) string {
	inputRunes := []rune(s)
	outputRunes := make([]rune, 0, len(inputRunes))
	for _, r := range inputRunes {
		outputRunes = append(outputRunes, ToggleRune(r))
	}
	return string(outputRunes)
}

// Strtoi is a wrapper of `strconv.Atoi()`.
// If `strconv.Atoi()` returns an error, Strtoi calls panic.
func Strtoi(s string) int {
	if i, err := strconv.Atoi(s); err != nil {
		panic(errors.New("[argument error]: Strtoi only accepts integer string"))
	} else {
		return i
	}
}

// LowerBound returns an index of a slice whose value is EQUAL TO AND LARGER THAN A KEY VALUE.
func LowerBound(s []int, key int) int {
	isLarger := func(index, key int) bool {
		if s[index] >= key {
			return true
		} else {
			return false
		}
	}

	left, right := -1, len(s)

	for right-left > 1 {
		mid := left + (right-left)/2
		if isLarger(mid, key) {
			right = mid
		} else {
			left = mid
		}
	}

	return right
}

// UpperBound returns an index of a slice whose value is EQUAL TO AND SMALLER THAN A KEY VALUE.
func UpperBound(s []int, key int) int {
	isSmaller := func(index, key int) bool {
		if s[index] <= key {
			return true
		} else {
			return false
		}
	}

	left, right := -1, len(s)

	for right-left > 1 {
		mid := left + (right-left)/2
		if isSmaller(mid, key) {
			left = mid
		} else {
			right = mid
		}
	}

	return left
}

// sort package (snippets)
//sort.Sort(sort.IntSlice(s))
//sort.Sort(sort.Reverse(sort.IntSlice(s)))
//sort.Sort(sort.Float64Slice(s))
//sort.Sort(sort.StringSlice(s))

// copy function
//a = []int{0, 1, 2}
//b = make([]int, len(a))
//copy(b, a)

/*******************************************************************/

var h, w int
var S [][]rune

func main() {
	tmp := NextIntsLine()
	h, w = tmp[0], tmp[1]
	for i := 0; i < h; i++ {
		row := NextRunesLine()
		S = append(S, row)
	}

	for i := 0; i < h; i++ {
		for j := 0; j < w; j++ {
			if S[i][j] == '#' {
				steps := [][]int{
					[]int{i + 1, j},
					[]int{i, j + 1},
					[]int{i, j - 1},
					[]int{i - 1, j},
				}
				canPaint := false
				for _, step := range steps {
					y, x := step[0], step[1]
					if 0 <= y && y < h && 0 <= x && x < w && S[y][x] == '#' {
						canPaint = true
						break
					}
				}
				if !canPaint {
					fmt.Println("No")
					return
				}
			}
		}
	}
	fmt.Println("Yes")
}