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 =))

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.