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: Runtime Error)

import java.util.*;
import java.io.*;

public class Main {
	
	static int w,h;
	static String [][]grid;
	static int counter=0;
	static int dp[][];
	
	public static int tr(Point a) {
		
		if((a.x==(w-1))&&(a.y==(h-1))) 
			return counter++;
		
			
		if(!valid(a))
			return -(int)1e9;
		
//		System.out.println("point : x : "+a.x+" y :"+a.y);
		Point down=new Point(a.x,a.y+1);
		Point right=new Point(a.x+1,a.y);
		
		try {
			if(dp[a.x][a.y]!=-1) {
				return dp[a.x][a.y];
			}
		}catch (Exception e) {
//			System.out.println("wrong!");
		}
		tr(down);
		tr(right);
//		dp[a.x][a.y]=tr(down);
//		dp[a.x][a.y]=tr(left);
		return (int) (counter%(1e9+7));
	}

	public static boolean valid(Point a) {
		
		try {
			if(grid[a.y][a.x]!=null) {
//				
				if(grid[a.y][a.x].equals("#")) 
					return false;
				
				if(grid[a.y][a.x].equals(".")) 
					return true;

					
			}
		}catch (Exception e) {

			return false;
			
		}
		
		return false;
	}
	public static void print(String [][]grid) {
		for (int i = 0; i < grid.length; i++) {
			for (int j = 0; j < grid[i].length; j++) {
				System.out.print(grid[i][j]);
			}
			System.out.println();
		}
	}
	public static void main (String[]args) throws IOException {
		 
		
		
		Scanner sc=new Scanner (System.in);
		PrintWriter pw=new PrintWriter(System.out);
		dp=new int [h][w];
		
		h=sc.nextInt();
		w=sc.nextInt();
		grid=new String[h][w];
		for(int i=0;i<h;i++) {
			for(int j=0;j<w;j++) {
				grid[i][j]=sc.next();
				
			}
		}
//		for(int i=0;i<h;i++) {
//			for(int j=0;j<w;j++) {
//				dp[i][j]=-1;
//				
//			}
//		}
		
//		print(grid);
//		for (int i = 0; i < h; i++) {
//			for (int j = 0; j < w; j++) {
//				pw.print(" i: "+i+" j:"+j+"-"+ tr(new Point(i,j)));
//				counter=0;
//			}
//		}
		pw.print( tr(new Point(0,0)));
		counter=0;
//		pw.print(valid(new Point(0,0)));
		pw.close();
		
	}
	static class Scanner {
		BufferedReader br;
		StringTokenizer st;
		public Scanner(InputStream s) {
			br = new BufferedReader(new InputStreamReader(s));
		}
		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 double nextDouble() throws IOException {
			return Double.parseDouble(next());
		}
		public int[] nextIntArr(int n) throws IOException {
			int[] arr = new int[n];
			for (int i = 0; i < n; i++) {
				arr[i] = Integer.parseInt(next());
			}
			return arr;
		}
	}
	static class Point{
		int x;
		int y;
		public Point(int x,int y) {
			this.x=x;
			this.y=y;
		}
	}
}