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#!/opt/local/bin/lua
--
-- See ../README.md
--
--
-- Run as: lua ch-2.lua < input-file
--
--
-- See ../README.md
--
--
-- This determines on which side of the line through (x1, y1) and
-- (x2, y2) the origin lies. If > 0, then the origin lies to the left
-- of the line, if < 0, the origin lies to the right of the line, if
-- = 0, the origin lies on the line.
--
function side (x1, y1, x2, y2)
return (y2 - y1) * x2 - (x2 - x1) * y2
end
for line in io . lines () do
--
-- Parse input
--
local _, _, x1, y1, x2, y2, x3, y3 =
line : find ("(%S+) (%S+) (%S+) (%S+) (%S+) (%S+)")
--
-- Determine where the origin is relative to the three lines
-- through the vertices of the triangle. Note we have to go
-- in a specific order through the points. (Either clock wise,
-- or counter clockwise, as long as we're consistent).
--
local s1 = side (x2, y2, x3, y3)
local s2 = side (x3, y3, x1, y1)
local s3 = side (x1, y1, x2, y2)
--
-- If the origin either lies to the left (or on) each of the
-- lines, or to the right (or on) each of the lines, the origin
-- lies inside the triangle. If not, it does not.
--
if (s1 <= 0 and s2 <= 0 and s3 <= 0) or
(s1 >= 0 and s2 >= 0 and s3 >= 0)
then print (1)
else print (0)
end
end
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