http://mtsmfm.github.io/2017/03/04/doukaku-e12.html への yancya の回答

main.rb

PATTERNS = {
  'I' => [[0],       [4]      ],
  'L' => [[0, 0],    [3, 1]   ],
  'O' => [[0, 0],    [2, 2]   ],
  'S' => [[1, 1, 0], [0, 1, 1]],
  'T' => [[0, 1, 0], [1, 1, 1]]
}

def hoge(str)
  minos = str.scan(/\d+[IOLST]/).map do |s|
    _, num, sym = /(\d+)([IOLST])/.match(s).to_a
    [num.to_i, sym]
  end

  a = [0] * (minos.map(&:first).max + 3)

  minos.each do |num, sym|
    pre, post = PATTERNS[sym]
    nums = a[num, pre.size]
    a[num, pre.size] = nums.zip(pre).map(&:sum).max.tap do |max|
      break post.map { |n| max + n }
    end
  end

  a.map(&:to_i).max.to_s
end

require 'test-unit'

class HogeTest < Test::Unit::TestCase
  TEST_CASES = DATA.each_line.map { |line|
    %r[^/\*(?<id>\d+)\*/.*test\((?<act_exp>.*)\)] =~ line
    act, exp = act_exp.scan(%r["(.+?)"]).flatten
    [id, [act, exp]]
  }.to_h

  data(TEST_CASES)
  test "hoge" do |(actual, expected)|
    assert { hoge(actual) == expected }
  end
end

__END__
/*0*/ test("1O3L0I0T", "5")
/*1*/ test("0I", "4")
/*2*/ test("0I0I", "8")
/*3*/ test("0I1I2I3I4I", "4")
/*4*/ test("0S0I", "5")
/*5*/ test("0I0S", "6")
/*6*/ test("2S0T2O3I", "8")
/*7*/ test("4O4T1T0S4L1L3L", "10")
/*8*/ test("0S2S4S6S8S10S12S14S", "16")
/*9*/ test("14S12S10S8S6S4S2S0S", "2")
/*10*/ test("5I2O10I0O4L10T9T11L8I2I10I12O7L12T12T12S11T9O10O13I12O10O7I9I7O0S1O2S0L1L", "23")
/*11*/ test("9T14L10L8T4I1T3S5I8T12O3S7L9O7L14T2I7O3S6S2L0L13T10O4I9T7L8S0I12O9S11L11T14T", "27")
/*12*/ test("9S9S7O11O16I2T9O12L10T9O0O13I9O1I2T14S7O9S11T5L7I14T13O0T12I3S10L10O7I15I6S2L12S8I16I3L", "23")
/*13*/ test("11T13I16S15T7O10L12S1I5I8S5I13I15O8S9I1T12I1S5S0L14I12L16T2S2S8L2S14L16O4I13L15L13S11S9T13S9S3L6O", "22")
/*14*/ test("12L10S7I5L14T12S9L1T14I0I5L1T2O18T9L0I15I16L10S1O15I0L17O5L18T4I18L7L7I13I3I12I2S3T5T3S16L14S14O11O15T14S", "17")
/*15*/ test("0S18S2S19I14T7L14L2L6I9I0L4I5L13L15I8S8T2I5I7O18T3S1T7I2L8O0S20T9I14T5L5I1T4L9O8T19T5S12O16T19L4O10O10T14L", "24")
/*16*/ test("7T5L6S4S8T6S10I19O20L14I18L21S7I11S11O1L13T20O9I7L2T8L2S20L3O14L9T17I8L8S14I6T2O11T21O18O6T15T1S3L6O19S18O20S19O16T6S14T", "26")
/*17*/ test("18S2I4S16L13S17I21O8I17T8I14O12T20I20S19S16S13T12T20I22I15O2I2I8I2S18I9I9T6O13O13L17I2L20L2L4I9I19O11T3S10O2S18T12I5O11S19O21S6I17T17S", "26")
/*18*/ test("11L5S0T22S18O13T2O22S15I12I21T16I3I1I22L11L11L22O13S24S15L13T15S19L10O15T7S24T19L0T13O11I12T13S4I24L15O3S19O10L19O0S20L7O11L21I22S18T19T23O8I22S24L0S", "21")
/*19*/ test("7L7I11T7S18O17L8S15L9I3O24S3O1O5O14L9T13S2O25S22T10T8L24S18S13T1O1L6I10I4S13O3S7L10T1T4L17S20I18O15S25S23S21I19T6O24S9L2O2O15L12L8L8O18I18L0T5O", "31")
/*20*/ test("999I999I999I999I999I999I999I999I999I999I999I", "44")