function uniquePaths(m: number, n: number): number {
    const f: number[][] = Array(m)
        .fill(0)
        .map(() => Array(n).fill(0));
    f[0][0] = 1;
    for (let i = 0; i < m; ++i) {
        for (let j = 0; j < n; ++j) {
            if (i > 0) {
                f[i][j] += f[i - 1][j];
            }
            if (j > 0) {
                f[i][j] += f[i][j - 1];
            }
        }
    }
    return f[m - 1][n - 1];
}