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javacircular-buffer

Scroll backward circular array

I have an array and I want to scroll the positions in it backward.

I have a boolean array and I need to count how many true are there from a given cell going forward and backward.

I know that if N is the number of elements into the array, I can go ahead doing i=(i+1)%N. But what if I need to scroll it in the opposite way?

Thank you in advance.

Solution

  • This should do it:

    i--;
if (i == -1)
  i = N-1;

    Or in 1 line:

    i = ((i-1 == -1) ? N-1 : i-1);

    But noise's variation of the above is probably better. A related if-statement version:

    if (i == 0)
  i = N-1;
else
  i--;

    A related 1-line version:

    i = (i == 0 ? N-1 : i-1)