递推

#include <iostream>
#include <vector>
#include <string>
using namespace std;
int main() {
    int r, c;
    cin >> r >> c;
    vector<string> grid(r);
    for (int i = 0; i < r; ++i) {
        cin >> grid[i];
    }
    vector<vector<int>> ways(r, vector<int>(c, 0));
    vector<int> prevWays(2, 0);
    ways[0][0] = 1;
    for (int i = 1; i < r; ++i) {
        prevWays[0] = 0;
        prevWays[1] = 0;
        for (int j = 1; j < c; ++j) {
            for (int k = 0; k < i; ++k) {
                prevWays[grid[k][j - 1] == 'R' ? 0 : 1] += ways[k][j - 1];
            }
            ways[i][j] = prevWays[grid[i][j] == 'R' ? 1 : 0];
        }
    }
    cout << ways[r - 1][c - 1] << endl;
    return 0;
}