Using the Stack ADT to Return Every Third Element
How can we return every third element from a stack?
How do we apply the steps provided to the example stack of 1 2 3 4 5 6 7 8 9?
Answer:
To return every third element from a stack, we can follow the steps outlined:
- Create a temporary stack to store elements that will be skipped.
- Initialize a count variable to track the number of elements processed.
- Iterate through the original stack, popping elements and checking the count.
- Create a result stack to store elements in the desired order.
- Iterate through the temporary stack to retrieve elements.
- Output the elements from the result stack in the desired order.
Using the steps provided, let's apply them to the given example stack of 1 2 3 4 5 6 7 8 9:
- Create a temporary stack and initialize count to 0.
- Iterate through the original stack:
- Pop 9, increment count to 1.
- Pop 8, increment count to 2.
- Pop 7, increment count to 3. Since count is a multiple of three, push 7 to the temporary stack.
- Pop 6, increment count to 4.
- Pop 5, increment count to 5.
- Pop 4, increment count to 6. Since count is a multiple of three, push 4 to the temporary stack.
- Pop 3, increment count to 7.
- Pop 2, increment count to 8.
- Pop 1, increment count to 9. Since count is a multiple of three, push 1 to the temporary stack.
- Create a result stack.
- Iterate through the temporary stack:
- Pop 1 from temporary stack, push to result stack.
- Pop 4 from temporary stack, push to result stack.
- Pop 7 from temporary stack, push to result stack.
- Iterate through the result stack and output the elements in the desired order: 7, 4, 1.
This process allows us to efficiently return every third element from the stack by using auxiliary data structures and counting elements.