renritsu.rb

MATCH_EQ = /(-?)([0-9]*)x(\+|-)([0-9]*)y=(-?)([0-9]+)/

def parse_equation(eq)
  unless eq.match(MATCH_EQ)
    raise "unsupported"
  end

  x = 0
  y = 0
  xsig   = $1
  xcoeff = $2
  ysig   = $3
  ycoeff = $4
  rhssig = $5
  rhs    = $6.to_i

  if xcoeff.empty?
    xcoeff = 1
  end
  if xsig.empty?
    x = xcoeff.to_i
  else
    x = -xcoeff.to_i
  end
  if ycoeff.empty?
    ycoeff = 1
  end
  if ysig == '+'
    y = ycoeff.to_i
  else
    y = -ycoeff.to_i
  end
  if rhssig.empty?
    rhssig = 1
  else
    rhssig = -1
  end

  return [x, y, rhssig*rhs]
end

puts "first equation?"
x, y, rhs = parse_equation(gets)
p [x, y, rhs]
puts "second equation?"
x2, y2, rhs2 = parse_equation(gets)
p [x2, y2, rhs2]

require 'matrix'
mat_A = Matrix[
  [ x,  y],
  [x2, y2],
]
mat_B = Matrix[
  [rhs],
  [rhs2]
]
begin
  mat_A_dash = mat_A.inverse
rescue ExceptionForMatrix::ErrNotRegular => e
  raise "その連立方程式は解けません"
end
ans = mat_A_dash * mat_B
puts <<EOS
  x = #{ans[0, 0]}
  y = #{ans[1, 0]}
EOS