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.IOException;
import java.io.InputStreamReader;
import java.lang.reflect.Array;
import java.util.*;

class Main{

	public static void main(String[] args) {
		FastReader f = new FastReader();
		int h = ii(f), w = ii(f);
		String[] str = new String[h];
		long[][] dp = new long[h][w];
		boolean f1, f2;
		for(int i=0; i<h; i++)
			str[i] = f.nextLine();
		dp[0][0] = 1;
		for(int i=0; i<h; ++i){
			for(int j=0; j<w; ++j){
				if(i == 0 && j == 0)
					continue;;
				f1 = j == 0 || str[i].charAt(j-1) == '#';
				f2 = i == 0 || str[i-1].charAt(j) == '#';
				if(!f1 && !f2)
					dp[i][j] = (dp[i-1][j] % MOD) + (dp[i][j-1] % MOD) % MOD;
				else if(f1 && f2)
					dp[i][j] = 0;
				else if(f1)
					dp[i][j] = dp[i-1][j];
				else
					dp[i][j] = dp[i][j-1];
			}
		}
		System.out.println(dp[h-1][w-1] % MOD);

	}

	static class FastReader {
		BufferedReader br;
		StringTokenizer st;

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

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		long nextLong() {
			return Long.parseLong(next());
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}
	}

	public static int ii(FastReader fr) {
		return fr.nextInt();
	}

	static long il(FastReader fr) {
		return fr.nextLong();
	}

	static double id(FastReader fr) {
		return fr.nextDouble();
	}

	static void printArray(Object[] arr) {
		for (Object x : arr)
			print(x, " ");
		printn("");
	}

	static void print(Object s, String sep) {
		System.out.print(s + sep);
	}

	static void printn(Object s) {
		System.out.println(s);
	}

	static long[] inputArrL(int n, FastReader fr) {
		long[] arr = new long[n];
		for (int i = 0; i < n; i++)
			arr[i] = fr.nextLong();
		return arr;
	}

	static int[] inputArr(int n, FastReader fr) {
		int[] arr = new int[n];
		for (int i = 0; i < n; i++)
			arr[i] = fr.nextInt();
		return arr;
	}

	static int max(int... args) {
		int max = Integer.MIN_VALUE;
		for (int x : args) {
			max = Math.max(x, max);
		}
		return max;
	}

	static int min(int... args) {
		int min = Integer.MAX_VALUE;
		for (int x : args) {
			min = Math.min(x, min);
		}
		return min;
	}

	static long max(long... args) {
		long max = Integer.MIN_VALUE;
		for (long x : args) {
			max = Math.max(x, max);
		}
		return max;
	}

	static long min(long... args) {
		long min = Integer.MAX_VALUE;
		for (long x : args) {
			min = Math.min(x, min);
		}
		return min;
	}

	static int lenDigit(int d) {
		if (d == 0)
			return 1;
		int l = 0;
		while (d != 0) {
			l++;
			d /= 10;
		}
		return l;
	}

	static int MOD = 1000000007;

}