There is no "stack size in C++" or "stack size in Java" — these values could be configured at compilation / runtime (though at TopCoder you, perhaps, could not control it).

You wrote:

Stack size for last test cases is roughly 25600. Is it that Java's available stack size is less than this?

But stack size is not measured in stack frames. Stack size is defined in bytes (and sometimes you can change this setting, for example from command line) — and it depends on your implementation how much each stack frame takes. For example you could try and make the method static, or use arguments of smaller size (shorts, for example). However, I do not believe such monkeying is a good approach.

I think when you see that recursion could be too deep, you need to use external stack (and iteration) or something like it. It would never do to write programs which are at the edge of failing by design.

Try this

new Thread(null, new Runnable() {
            public void run() {
                new Main().run();
            }
        }, "1", 1 << 23).start();

Executes .run() method with 8Mb stacksize. (Last parametr == (1 << 23) )