082 Path sum three ways.sf

#!/usr/bin/ruby

# Author: Daniel "Trizen" Șuteu
# License: GPLv3
# Date: 08 August 2016
# Website: https://github.com/trizen

# The minimal path sum in the 5 by 5 matrix below, by starting in any cell
# in the left column and finishing in any cell in the right column, and only
# moving up, down, and right; the sum is equal to 994.

# Find the minimal path sum, in a 31K text file containing a 80 by 80 matrix,
# from the left column to the right column.

# https://projecteuler.net/problem=82

# usage: sidef script.sf < p082_matrix.txt

var matrix = []
ARGF.each { |line|
    matrix << line.trim.split(',').map{ .to_n }
}

var end = matrix.end

func path(i, j, prev='ok') is cached {

    j >= end && return matrix[i][j]

    var paths = []
    if (i>0 && prev!='down') {
        paths << path(i-1, j, 'up')
    }

    paths << path(i, j+1)

    if (i<end && prev!='up') {
        paths << path(i+1, j, 'down')
    }

    paths.min + matrix[i][j]
}

say (0..end -> map {|i| path(i, 0) }.min)