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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {
	final static int MOD = 1000000007;
	public static void main(String[] args) {
		Reader in = new Reader();
		int n = in.nextInt();
		int m = in.nextInt();
		char[][] v = new char[n][m];
		int[][] dp = new int[n][m];
		for(int i  = 0; i<n; i++) {
			char[] a = in.next().toCharArray();
			for(int j = 0; j<m; j++)  v[i][j] = a[j];
		}
		dp[0][0] = 1;
		for(int i = 1; i<n; i++) if(v[i][0]=='#') dp[i][0] = 0; else dp[i][0] = dp[i-1][0];
		for(int j = 1; j<m; j++) if(v[0][j]=='#') dp[0][j] = 0; else dp[0][j] = dp[0][j-1];
			
		for(int i = 1; i<n; i++) {
			for(int j = 1; j<m; j++) {
				dp[i][j] += dp[i-1][j];
				dp[i][j]%=MOD;
				dp[i][j] += dp[i][j-1];
				dp[i][j]%=MOD;
				if(v[i][j]=='#') dp[i][j] = 0;
			}
		}
		System.out.println(dp[n-1][m-1]);
	}
	
	static class Reader {
		static BufferedReader br;
		static StringTokenizer st;
		private int charIdx = 0;
		private String s;

		public Reader() {
			this.br = new BufferedReader(new InputStreamReader(System.in));
		}

		public int[] na(int n) {
			int[] a = new int[n];
			for (int i = 0; i < n; i++)
				a[i] = nextInt();
			return a;
		}

		public char nextChar() {
			if (s == null || charIdx >= s.length()) {
				if (st == null || !st.hasMoreTokens())
					try {
						readLine();
					} catch (Exception e) {
					}
				s = st.nextToken();
				charIdx = 0;
			}
			return s.charAt(charIdx++);
		}

		public long[] nl(int n) {
			long[] a = new long[n];
			for (int i = 0; i < n; i++)
				a[i] = nextLong();
			return a;
		}

		public char[] nca() {
			return next().toCharArray();
		}

		public String[] nS(int n) {
			String[] a = new String[n];
			for (int i = 0; i < n; i++)
				a[i] = next();
			return a;
		}

		public int nextInt() {
			if (st == null || !st.hasMoreTokens())
				try {
					readLine();
				} catch (Exception e) {
				}
			return Integer.parseInt(st.nextToken());
		}

		public double nextDouble() {
			if (st == null || !st.hasMoreTokens())
				try {
					readLine();
				} catch (Exception e) {
				}
			return Double.parseDouble(st.nextToken());
		}

		public Long nextLong() {
			if (st == null || !st.hasMoreTokens())
				try {
					readLine();
				} catch (Exception e) {
				}
			return Long.parseLong(st.nextToken());
		}

		public String next() {
			if (st == null || !st.hasMoreTokens())
				try {
					readLine();
				} catch (Exception e) {
				}
			return st.nextToken();
		}

		public static void readLine() {
			try {
				st = new StringTokenizer(br.readLine());
			} catch (Exception e) {
			}
		}
	}
}