"How low can you go?"

(Hey, with that title I can just keep my mouth shut and young people will think I'm quoting Ludacris, while old people will think I'm quoting Chubby Checker! Oops...)

So I decided to create a dummy version of the program that instead of calculating the number of "fair and square" numbers in a given range, just adds the low and high end of the range and prints it out, using the format the Code Jam problem requires:

numXs :: Integer -> Integer -> Integer

numXs a b = a + b

-- jagd's main, which I believe is set up to read stdin

solve i num = do
    [a, b] <- getLine >>= return . map read . words
    putStrLn $ "Case #" ++ show i ++ ": " ++ (show $ numXs a b)
    if i < num
       then solve (i+1) num
       else return ()

main = do
   num <- getLine >>= return.read
   solve 1 num

Compiled it up with -O2 and ran...

time ./dummy <C-large-practice-2.in >woof.dummy

real    0m0.106s
user    0m0.092s
sys     0m0.012s

Here the variance is a hefty factor; one run took 0.171 seconds!

The surprising part of the profiling was the memory allocation:

total alloc = 196,851,848 bytes  (excludes profiling overheads)

Compare that with the real program:

total alloc = 546,422,264 bytes  (excludes profiling overheads)

The full program is allocating lists of powers of ten, and potentially over 50,00040,000 Y values! There's something very inefficient going on in solve.

UPDATE: There must be a difference between "total alloc" and memory usage. Running dummy with the options to track memory usage shows memory usage peaking at maybe 60K, compared with the palindrome program, which peaks quickly at around 4M. Both programs must be allocating and freeing quite a lot, the difference being that we save up those lists of Ys and powers of ten.


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