Project Euler 18 in ruby

triangle = [
%w!75!,
%w!95 64!,
%w!17 47 82!,
%w!18 35 87 10!,
%w!20 04 82 47 65!,
%w!19 01 23 75 03 34!,
%w!88 02 77 73 07 63 67!,
%w!99 65 04 28 06 16 70 92!,
%w!41 41 26 56 83 40 80 70 33!,
%w!41 48 72 33 47 32 37 16 94 29!,
%w!53 71 44 65 25 43 91 52 97 51 14!,
%w!70 11 33 28 77 73 17 78 39 68 17 57!,
%w!91 71 52 38 17 14 91 43 58 50 27 29 48!,
%w!63 66 04 68 89 53 67 30 73 16 69 87 40 31!,
%w!04 62 98 27 23 09 70 98 73 93 38 53 60 04 23!,
]

# I can modify the triangle is I go up, and then simply return the first element

def left_col(col)
  if col == 0
    0
  else
    col
  end
end

# Start from the n-1 row
(triangle.size - 2).downto(0) do |row|
  0.upto(row) do |col|
    left = triangle[row + 1][ left_col(col) ].to_i
    right = triangle[row + 1][ col + 1 ].to_i
    
    triangle[row][col] = triangle[row][col].to_i + [left,right].max
  end
end