For the following problem 543A - Writing Code, the jury's solution 11035704 optimize the DP solution explained in the contest's editorial http://codeforces.me/blog/entry/17773.

I understood the approach explained in the editorial, but what's the intuition behind the optimization and how it works? Specially the lines with bitwise operations:

    int i = it & 1;
        ...
        z[i][j][k] = z[i ^ 1][j][k];
  ...
    ans += z[n & 1][bl][i];
  ...

Thanks.