I am trying to take an online course of algorithms and i cant seem to get my head around how this works. (this is not homework, just a question from a free online course)
would anyone explain to me how the answers are found? the are given at the end of the exercise but i do not understand how it works. thanks in advance ! :)
Suppose that an intermixed sequence of (stack) push and pop operations are performed. The pushes push the integers 0 through 9 in order; the pops print out the return value. Which of the following sequence(s) could not occur? (a) 4 3 2 1 0 9 8 7 6 5
(b) 4 6 8 7 5 3 2 9 0 1
(c) 2 5 6 7 4 8 9 3 1 0
(d) 4 3 2 1 0 5 6 7 8 9
(e) 1 2 3 4 5 6 9 8 7 0
(f) 0 4 6 5 3 8 1 7 2 9
(g) 1 4 7 9 8 6 5 3 0 2
(h) 2 1 4 3 6 5 8 7 9 0
Correct Answers: (b), (f), and (g).