I had to run this through the debugger to understand what the nature of arrLn is.
In my solution I was rewriting the whole pyramide, but all my variables rot away after using them once.
Thanks for your solution

Exacly, it's very nice =))

I like how you multiply the result by 256 before adding the parsed value.
I shifted my parsed value and then added it to the result.
Your solution looks way nicer :)

Good solution, but remember, for performance, that StringBuffer's usage must be restricted to when the variable is used in more than one thread. That's not the case here, which should be used StringBuilder.

Nice job, very quick!

You need not initialize arrLn[i] = 0 in java, since int being a primitive type is Initialized to 0 anyhow.
Apart from that, it's the perfect solution. No side effect to the original input array, neither you have created a copy of the array.