A.(rear - 1)% n == front B.(rear + 1)% n == front C.(front - 1)% n == rear D.(front + 1)% n == rear
A.rear = rear+1 B.rear = (rear+1)%m C.front = (front+1)%m D.rear = (rear+1)%m + 1
A.n十1 B.n C.n-1 D.n-2