Code Golf: Lights out

Answer 1

Lua, 499 characters

Fast, uses Strategy to find a quicker solution.

m={46,[42]=88,[46]=1,[88]=42}o={88,[42]=46,[46]=42,[88]=1}z={1,[42]=1}r=io.read
l=r()s=#l q={l:byte(1,s)}
for i=2,s do q[#q+1]=10 l=r()for j=1,#l do q[#q+1]=l:byte(j)end end
function t(p,v)q[p]=v[q[p]]or q[p]end
function u(p)t(p,m)t(p-1,o)t(p+1,o)t(p-s-1,o)t(p+s+1,o)end
while 1 do e=1 for i=1,(s+1)*s do
if i>(s+1)*(s-1)then if z[q[i]]then e=_ end
elseif z[q[i]]then u(i+s+1)end end
if e then break end
for i=1,s do if 42==q[i]or 46==q[i]then u(i)break end u(i)end end
print(string.char(unpack(q)))

Example input:

.....
.....
.....
.....
*...*

Example output:

XX...
..X..
X.XX.
X.X.X
...XX