015 Lattice paths.sf

#!/usr/bin/ruby

# Author: Daniel "Trizen" Șuteu
# License: GPLv3
# Website: https://github.com/trizen

# Starting in the top left corner of a 2×2 grid, and only being able to move to the right and down, there are exactly 6 routes to the bottom right corner.
# How many such routes are there through a 20×20 grid?

# https://projecteuler.net/problem=15

# Runtime: 0.131s

func lattice_paths(n) {
    binomial(2*n, n);
}

say lattice_paths(20);