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local input = {}
for line in io.lines() do
local row = {}
for i = 1,#line do
-- X,M,A,S --> 1,2,3,4
row[i] = string.find('XMAS', string.sub(line, i, i)) or 0
end
table.insert(input, row)
end
function compute_bounds (dx, size)
return math.max(0, -3*dx)+1, math.min(size, size-3*dx)
end
function input:_has_xmas (i, j, di, dj)
for x = 0,3 do
if self[i+x*di][j+x*dj] ~= x+1 then
return false
end
end
return true
end
function input:part1 ()
local m = #self
local n = 0
if m ~= 0 then n = #self[1] end
local sum = 0
for di = -1,1 do
local istart, iend = compute_bounds(di, m)
for dj = -1,1 do
if di ~= 0 or dj ~= 0 then
local jstart, jend = compute_bounds(dj, n)
for i = istart,iend do
for j = jstart,jend do
if self:_has_xmas(i, j, di, dj) then
sum = sum + 1
end
end
end
end
end
end
print(sum)
end
function input:_has_x_mas (i, j)
if self[i][j] ~= 3 then return false end
local nm = 0
for ci = i-1,i+1,2 do
for cj = j-1,j+1,2 do
if self[ci][cj] == 2 then
nm = nm + 1
if nm > 2 then return false end
elseif self[ci][cj] ~= 4 then
return false
end
end
end
return nm == 2 and self[i-1][j-1] ~= self[i+1][j+1]
end
function input:part2 ()
local m = #self
local n = 0
if m ~= 0 then n = #self[1] end
local sum = 0
for i = 2,m-1 do
for j = 2,n-1 do
if self:_has_x_mas(i, j) then sum = sum + 1 end
end
end
print(sum)
end
return input
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