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### COS 226 Exercises on Stacks and Queues

*Reference: Section 4.3 in Introduction to Programming in Java *

**1. **
A letter means enqueue and an asterisk means dequeue in the sequence
`E A S * Y * Q U E * * * S T * * * I O * N * * *`
Give the sequence of values returned by the dequeue operations when this
sequence of operations is performed on an initially empty FIFO queue.

**2. **
Suppose that a client performs an intermixed sequence of (stack) *push*
and *pop* operations. The push operations push the integers 0 through 9
in order on to the stack; the pop operations print out the return value.
Circle the following sequence(s) that could *not* occur.

a. 4 3 2 1 0 9 8 7 6 5
b. 2 1 4 3 6 5 8 7 9 0
c. 0 4 6 5 3 8 1 7 2 9
d. 4 6 8 7 5 3 2 9 0 1