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#!/usr/bin/env lua
--[[
Challenge 093
TASK #1 > Max Points
Submitted by: Mohammad S Anwar
You are given set of co-ordinates @N.
Write a script to count maximum points on a straight line when given
co-ordinates plotted on 2-d plane.
Example 1:
|
| x
| x
| x
+ _ _ _ _
Input: (1,1), (2,2), (3,3)
Output: 3
Example 2:
|
|
| x x
| x
| x x
+ _ _ _ _ _
Input: (1,1), (2,2), (3,1), (1,3), (5,3)
Output: 3
--]]
function get_points()
if #arg < 6 or math.fmod(#arg, 2) ~= 0 then
io.write("Usage: ch-1.lua x y x y x y ...\n")
os.exit(1)
end
local P = {}
for i=1, #arg, 2 do
local x = tonumber(arg[i])
local y = tonumber(arg[i+1])
table.insert(P, {x,y})
end
return P
end
function in_line(pi, pj, pk)
-- compute cross product
dxc = pk[1] - pi[1];
dyc = pk[2] - pi[2];
dxl = pj[1] - pi[1];
dyl = pj[2] - pi[2];
cross = dxc * dyl - dyc * dxl;
return cross == 0 and true or false
end
function max_in_line(P)
local max_count = 0
-- for each pair
for i=1, #P-1 do
for j=i+1, #P do
-- check other points against pair
local count = 0
for k=1, #P do
if in_line(P[i], P[j], P[k]) then
count = count + 1
end
end
max_count = math.max(max_count, count)
end
end
return max_count
end
io.write(max_in_line(get_points()), "\n")
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