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#!/usr/bin/env lua
--[[
Challenge 101
TASK #2 � Origin-containing Triangle
Submitted by: Stuart Little
You are given three points in the plane, as a list of six co-ordinates:
A=(x1,y1), B=(x2,y2) and C=(x3,y3).
Write a script to find out if the triangle formed by the given three
co-ordinates contain origin (0,0).
Print 1 if found otherwise 0.
--]]
function sign(x1,y1,x2,y2,x3,y3)
return (x1 - x3) * (y2 - y3) - (x2 - x3) * (y1 - y3)
end
function point_in_triangle(xp,yp, x1,y1,x2,y2,x3,y3)
local d1 = sign(xp,yp, x1,y1, x2,y2)
local d2 = sign(xp,yp, x2,y2, x3,y3)
local d3 = sign(xp,yp, x3,y3, x1,y1)
local has_neg
if (d1 < 0) or (d2 < 0) or (d3 < 0) then
has_neg = true
else
has_neg = false
end
local has_neg = (d1 < 0) or (d2 < 0) or (d3 < 0)
local has_pos = (d1 > 0) or (d2 > 0) or (d3 > 0)
if has_neg and has_pos then
return 0
else
return 1
end
end
io.write(point_in_triangle(0,0,
tonumber(arg[1]), tonumber(arg[2]),
tonumber(arg[3]), tonumber(arg[4]),
tonumber(arg[5]), tonumber(arg[6])), "\n")
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