A.a[0][2*1] B.a[1][3] C.a[4-2][0] D.a[0][4]
A.intN=5,b[N][N]; B.inta[1][2]={{1},{3}}; C.intc[2][]={{1,2},{3,4}}; D.intd[3][2]={{1,2},{3,4}};
A.O(1) B.O(n) C.O(nlog2n) D.O(n*n)