For j=7 To 3 Step -1
If a(j-2) > a(j) Then
t=a(j-2): a(j-2)=a(j): a(j)=t
End If
Next j
数组元素a(1)到a(7)的值依次为“1, 4,5,2,7,6,3”,执行该程序段后,元素交换的次数为( )