/**
 * A bi-directional bubble sort demonstration algorithm
 */
class BBS extends SortAlgorithm {
    void sort(int a[]) throws Exception {
	int j;
	int limit = a.length;
	int st = -1;
	while (st < limit) {
	    boolean flipped = false;
	    st++;
	    limit--;
	    for (j = st; j < limit; j++) {
		if (stopRequested) {
		    return;
		}
		if (a[j] > a[j + 1]) {
		    int T = a[j];
		    a[j] = a[j + 1];
		    a[j + 1] = T;
		    flipped = true;
		    pause(st, limit, j, j+1);
		}
	    }
	    if (!flipped) {
		return;
	    }
	    for (j = limit; --j >= st;) {
		if (stopRequested) {
		    return;
		}
		if (a[j] > a[j + 1]) {
		    int T = a[j];
		    a[j] = a[j + 1];
		    a[j + 1] = T;
		    flipped = true;
		    pause(st, limit, j, j+1);
		}
	    }
	    if (!flipped) {
		return;
	    }
	}
	pause(0,a.length,-1,-1);
    }
}