Outputs max distance you can travel where t is destination count, k is distance, and ls is a list of length.

choose_best_trip.rb

def choose_best_trip(t, k, ls)
  ls.combination(k).to_a.map{|a| a.reduce(:+)}.select{ |v| v <= t }.max
end

# example: ts = [50, 55, 56, 57, 58] choose_best_trip(163, 3, ts) -> 163

# Tests

Test.describe("choose_best_sum") do
    Test.it("Basic Tests") do
        ts = [50, 55, 56, 57, 58]
        Test.assert_equals(choose_best_trip(163, 3, ts), 163)
        ts = [50]
        Test.assert_equals(choose_best_trip(163, 3, ts), nil)
        ts = [91, 74, 73, 85, 73, 81, 87]
        Test.assert_equals(choose_best_trip(230, 3, ts), 228)
    end
end