165 Только вправо или вниз - Динамика

#include <stdio.h>

int main( )
{
    FILE *in = fopen("input.txt", "rt");
    FILE *out = fopen("output.txt", "wt");

    if (in && out)
    {
        int n, m;
        fscanf(in, "%d %d", &n, &m);

        int arr[n][m], mat[n][m];

        for (int i = 0; i < n; ++i)
        {
            for (int j = 0; j < m; ++j)
            {
                fscanf(in, "%d", &arr[i][j]);
                mat[i][j] = 0;
            }
        }
        mat[0][0] = 1;

        for (int i = 0; i < n; ++i)
        {
            for (int j = 0; j < m; ++j)
            {
                if (mat[i][j] && arr[i][j])
                {
                    if (j + arr[i][j] < m)
                        mat[i][j + arr[i][j]] += mat[i][j];
                    if (i + arr[i][j] < n)
                        mat[i + arr[i][j]][j] += mat[i][j];
                }
            }
        }

        fprintf(out, "%d", mat[n-1][m-1]);
    }
    return 0;
}