Problem:
Score : 100 points

Problem Statement

There is a grid with H horizontal rows and W vertical columns.
Let (i, j) denote the square at the i-th row from the top and the j-th column from the left.

For each i and j (1 \leq i \leq H, 1 \leq j \leq W), Square (i, j) is described by a character a_{i, j}.
If a_{i, j} is ., Square (i, j) is an empty square; if a_{i, j} is #, Square (i, j) is a wall square.
It is guaranteed that Squares (1, 1) and (H, W) are empty squares.

Taro will start from Square (1, 1) and reach (H, W) by repeatedly moving right or down to an adjacent empty square.

Find the number of Taro's paths from Square (1, 1) to (H, W).
As the answer can be extremely large, find the count modulo 10^9 + 7.

Constraints

H and W are integers.

2 \leq H, W \leq 1000

a_{i, j} is . or #.

Squares (1, 1) and (H, W) are empty squares.

Input

Input is given from Standard Input in the following format:

H W
a_{1, 1}\ldotsa_{1, W}
:
a_{H, 1}\ldotsa_{H, W}

Output

Print the number of Taro's paths from Square (1, 1) to (H, W), modulo 10^9 + 7.

Sample Input 1

3 4
...#
.#..
....

Sample Output 1

3

There are three paths as follows:

Sample Input 2

5 2
..
#.
..
.#
..

Sample Output 2

0

There may be no paths.

Sample Input 3

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

Sample Output 3

24

Sample Input 4

20 20
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................

Sample Output 4

345263555

Be sure to print the count modulo 10^9 + 7.

Solution in Java (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.*;
import java.io.*;
 
public class Main {
 
	public static void main(String[] args) throws IOException,InterruptedException{
		Scanner sc=new Scanner(System.in);
		h=sc.nextInt();
		w=sc.nextInt();
		dp=new int[h][w];
		arr=new char[h][w];
		for (int i = 0; i < h; i++) {
			arr[i]=sc.next().toCharArray();
		}
		solve();
//		for (int i = 0; i < h; i++) {
//			for (int j = 0; j < w; j++) {
//				pw.print(dp[i][j]+" ");
//			}
//			pw.println();
//		}
		pw.println(dp[h-1][w-1]);
		pw.close();
    }
	static int h,w;
	static int[][] dp;
	static char[][] arr;
	static int mod=1000000007;
	static boolean isValid(int i, int j){
		return i >= 0 && i < h && j >= 0 && j < w && arr[i][j]=='.';
	}
	static void solve(){
		for (int x = 0; x < h; x++) {
			for (int y = 0; y < w; y++) {
				if (x==0&&y==0) {
					dp[x][y]=1;
				}
				else if(isValid(x,y-1)&&isValid(x-1,y)) {
					dp[x][y]=(dp[x-1][y]%mod+dp[x][y-1]%mod)%mod;
				}
				else if (isValid(x-1,y)) {
					dp[x][y]=dp[x-1][y]%mod;
				}
				else if (isValid(x,y-1)) {
					dp[x][y]=dp[x][y-1]%mod;
				}
			}
		}
	}
	static PrintWriter pw=new PrintWriter(System.out);
	static long pow(int a,int b) {
		long r=1l;
		for (int i = 0; i < b; i++) {
			r*=a;
		}
		return r;
	}
	static int[]lp;
	static void sieveLinear(int N){
		ArrayList<Integer> primes = new ArrayList<Integer>();
		lp = new int[N + 1];								//lp[i] = least prime divisor of i
		for(int i = 2; i <= N; ++i){
			if(lp[i] == 0){
				primes.add(i);
				lp[i] = i;
			}
			int curLP = lp[i];
			for(int p: primes)//all primes smaller than or equal my lowest prime divisor
				if(p > curLP || p * 1l * i > N)
					break;
				else
					lp[p * i] = p;
		}
	}
	static long gcd(int x,int y) {
		while (x!=y) {
			if(Math.max(x,y)/Math.min(x,y)==(double)(Math.max(x,y))/Math.min(x,y)) return Math.min(x,y);
			if(lp.length!=0) {
				if(lp[x]==x) {
					if(y/x==y/(double)x) return x;
					else return 1;
				}else if (lp[y]==y) {
					if(x/y==x/(double)y) return y;
					else return 1;
				}	
			}
			if(x>y) x-=y;
			else y-=x;
		}
		return x;
	}
	static class pair implements Comparable<pair> {
		int x;
		int y;
 
		public pair(int x, int y) {
			this.x = x;
			this.y = y;
		}
 
		public String toString() {
			return x + " " + y;
		}
		public boolean equals(Object o) {
            if (o instanceof pair) {
                pair p = (pair)o;
                return p.x == x && p.y == y;
            }
            return false;
        }
        public int hashCode() {
            return new Double(x).hashCode() * 31 + new Double(y).hashCode();
        }
        public int compareTo(pair other) {
        	if(this.x==other.x) {
        		return Long.compare(this.y, other.y);
        	}
			return Long.compare(this.x, other.x);
		}
	}
	static class tuble implements Comparable<tuble> {
		int x;
		int y;
		int z;
 
		public tuble(int x, int y, int z) {
			this.x = x;
			this.y = y;
			this.z = z;
		}
 
		public String toString() {
			return x + " " + y + " " + z;
		}
 
		public int compareTo(tuble other) {
			if (this.x == other.x) {
				if(this.y==other.y) return this.z - other.z;
				else return this.y - other.y;
			} else {
				return this.x - other.x;
			}
		}
	}
 	static class Scanner {
		StringTokenizer st;
		BufferedReader br;
 
		public Scanner(InputStream s) {
			br = new BufferedReader(new InputStreamReader(s));
		}
 
		public boolean hasNext() {
			// TODO Auto-generated method stub
			return false;
		}
 
		public String next() throws IOException {
			while (st == null || !st.hasMoreTokens())
				st = new StringTokenizer(br.readLine());
			return st.nextToken();
		}
 
		public int nextInt() throws IOException {
			return Integer.parseInt(next());
		}
 
		public long nextLong() throws IOException {
			return Long.parseLong(next());
		}
 
		public String nextLine() throws IOException {
			return br.readLine();
		}
 
		public double nextDouble() throws IOException {
			String x = next();
			StringBuilder sb = new StringBuilder("0");
			double res = 0, f = 1;
			boolean dec = false, neg = false;
			int start = 0;
			if (x.charAt(0) == '-') {
				neg = true;
				start++;
			}
			for (int i = start; i < x.length(); i++)
				if (x.charAt(i) == '.') {
					res = Long.parseLong(sb.toString());
					sb = new StringBuilder("0");
					dec = true;
				} else {
					sb.append(x.charAt(i));
					if (dec)
						f *= 10;
				}
			res += Long.parseLong(sb.toString()) / f;
			return res * (neg ? -1 : 1);
		}
 
		public boolean ready() throws IOException {
			return br.ready();
		}
 
	}
 
}