[BOJ 15241] Counting paths
View as PDFEvery afternoon, Jack runs from his house to John's. Their houses are in an open field of size N x M. Jack is trying to use a different path each day but he is not sure how many different ways to reach John's house exist.</p>
We will represent the field using a grid of N rows and M columns like the following:
.... ..X. ....
Jack lives in the top-left position and John in the bottom-right. Jack wants to use a different route every day but does not want to waste time he will only walk down and/or right. Also, some parts of the fields have obstacles such as rocks or houses and Jack cannot go through them (they are marked with an X in the grid).
In the previous field, the 4 valid routes are:
** ..X ... |
....X. ** |
... X. . |
.. .X. . |
Notice that all the valid routes will always have the same length (N + M - 1).
The number of possible paths can be very large so print the result modulo 1000000007 (10^9 + 7).
입력 형식
The first line will contain two integers N and M. The rows and columns of the map.</p>
Each of the following N lines will contain M characters. If the character is a dot (.), this position is empty. If the character is an X, it means that there is an obstacle and Jack cannot use this cell.
The top-left and bottom-right cells will never have an obstacle on them.
2 <= N <= 200
2 <= M <= 200
출력 형식
Print the number of possible path between the top-left and bottom-right positions. Remember to print the result modulo 1000000007.</p>
In most languages the modulus operator is %.
예제 입력 1
3 4
....
..X.
....
예제 출력 1
4
예제 입력 2
3 3
.X.
X..
...
예제 출력 2
0
예제 입력 3
5 5
.....
.....
.....
.....
.....
예제 출력 3
70
예제 입력 4
30 20
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....X...............
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............X.......
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예제 출력 4
833886024
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