Listing 2

(a)

X Modify = (N*M)
X Count  = 3
Y Modify = 1 - 2(N*M)  (negative)
Y Count =  (N*M)


(b)

0, (N*M), 2(N*M), 
1, (N*M)+1, 2(N*M)+1, 
2, (N*M)+2, 2(N*M)+2,
 ...
(N*M)-1, 2(N*M)-1, 3(N*M)-1,
0, ...