java - Homework: how to write own multiplication of big numbers? -

I want to multiply a large number of my project (maximum java.long) in my own BigNumber class as int [] . Actually I need to implement something like this:

  157 x 121 y ---- 157 Results 1 314 + result 2 157 + result 3 ------ 18997 final Result  

But how do I implement it?

I thought the result was zeros (3140, 15700) and adding them with the expansion of 2,3. But first I need to navigate between each of the y numbers and multiply it by every digit of x.

Fill the numbers.

  36 x 92 3 6 + ----- + ----- + | 2/5/9 | / | / | | / 7 | / 4 + ----- + ----- + | 0 / || 1/2 / | / | | / 6 | / 2 | + ----- + ----- +  

Add numbers to each diagonal Visit at least-important digits (lower right) more than (upper left).

  2 2 (at least-important) (6 + 1 + 4) = 11 (make it) 1, and move it to the next digit) 1 (5 + 7 + 0 + 1 (done) = 13 (make it 3, take 1) 3 2 +1 (recovered) = 3 3 (most important)  

Answer 3312

Create two-dimensional array of points.

Write some arguments to scrape the above diagonals.

This should work for arbitrarily large numbers (as long as you have left the memory).