Stack question: pop out in a pattern

At run time I want to input two types of datatype, double and string. One of the condition is that String should pop in the order I input, and double will pop as the usual stack behaviour, LIFO. Another condition is that the stack is limited to max size 10

E.g. one runtime example

Input Hello 1 World 2 blah blah 3 4 5

Output Hello 5 World 4 blah blah 3 2 1

My first question is how many ways is there to solve this problem? I have solved this problem using 3 stacks, one which stores double开发者_开发百科, one which store strings, and one which is used to reverse the string order.

I need to save the pattern so the program know which order the doubles comes, thus I save the pattern to the string stack. Since the stack is limited to size 10, I will need to save the pattern in another way.

So this is how my string stack will look like after the push

1. Hello*
2. World*
3. blah
4. blah***

So when at the first read I need to make specific read in that Stack position and just extract Hello out of it. Asterisk * is left for later use when I tell the program next pop is an double.

My second question is that I wonder if there is some other more elegant solution to this problem. Since my solution will involve some string manipulation to solve this problem. And as for now I'm not actually using the pop function in the string case as it is supposed to be used. I made the solution in C++ btw.

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What you're doing is fine, except that if you must use a stack, then you aren't allowed to access random locations in a stack -- you can only push/pop -- and also it's not so nice to modify the input strings and store asterisks in them.

You can solve this using only push/pop operations with 5 stacks (technically, only 4 will be used at any one time, but since they are of different types, you need to declare all 5 in your program):

stack 1: push doubles in input order

stack 2: push strings in input order

stack 3: push data types (double or string) in input order

stack 4: reverse the order of strings in stack 2

stack 5: reverse the order of data types in stack 3

Now pop one data type at a time from stack 5, if it is a double, pop from stack 1, otherwise pop from stack 5, and print the popped value.

Edit: @jleedev makes a good point that there isn't a general solution when the stack size is limited. What I've described above assumes that you're allowed to use multiple stacks and each stack can hold as many items as present in the input.

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I'll ignore the stack size constraint since I think it's meaning is unclear. In addition, if you can use multiple stacks all limited to size 10, then you can simulate larger stacks by using multiple actual stacks.

So, this can be done with 2 stacks using only push/pop.

1. push everything onto stack A.

2. pop everything from A onto B.

3. if B.empty return

4. if B.top is a double goto 7

5. output B.top and pop it off of B

6. goto 3

7. pop all of B onto A

8. while A.top is not a double pop A onto B

9. output A.top and pop it off of A

10. goto 2.