Page 1034 - AP Computer Science A, 7th edition

31. (B) Hand execute this for a 2×2 matrix. i goes from 0 to 0, j goes from 0 to 0, so the only interchange is swap mat[0][0] with mat[1][1], which suggests choice B. Check with a 3 × 3 matrix:
i= j 0 0
=
swap mat[0][0] with mat[2] [2]
swap mat[0][1] with mat[1] [2]
swap mat[1][0] with mat[2] [1]
i= j 1 0
=
j = 1
The elements to be interchanged are shown paired in the following figure. The result will be a reflection through the minor diagonal.