stack – Stack
Stack is a data structure providing two operations: “push” and “pop”. A push operation adds an item to the top of the stack and a pop operation removes an item from the top of the stack.
The stack data structure work like a physical stack such as for example a stack of books. You place items in a given order and they are removed in the reverse order that they are added. (FILO: first-in last-out.)
Stacks are useful in implementing several algorithms: depth-first search; call stacks; expression evaluation and parsing; memory management; etc.
In this exercise your task is to implement a command-line stack for numbers. Here is how your program should behave:
$ ./stack
push 6
push 2
pop
2
push 7
push 88
pop
88
pop
7
pop
6
After reading the command push <n>
your program should push the number <n> to the stack
and print nothing.
After reading the command pop
your program should remove the number at the top of the stack
and print it.
Input and output
Input contains several lines each with a stack operation
either push <n> or pop. The numbers given
on each push operation will all be integers.
For each pop operation listed on the input,
output should contain a number indicating what was popped.
If there are no values in the queue,
your program should print empty.
Input will be given so that there will be no more than 100 numbers stored in the stack at any given moment. Input is terminated by the end-of-file (EOF).
Example input
push 6
push 2
pop
push 7
push 88
pop
pop
pop
Example output
2
88
7
6
Scoring
- 1/6: works for the above example but produces output in an incorrect format
- 2/6: works for the above example and produces output in the correct format
- 5/6: works for other test cases
- 6/6: works for edge cases
Related exercises
try first: index-string repeat-list replace
try also: queue
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