Question

(java)

Write an algorithm that displays all the characters in a stack in the order in which they were pushed onto the stack. After all the characters are displayed, the stack should have the same contents as when you started. In your method, you can only use the stack’s operation, and NO explicit index can be declared to locate the items in the stack. Also, write the main() function to test your algorithm.

Answer 1

Hi,

Please refer screenshots for more clarity.

public static Stack printInOrder(Stack<Character>st): Recursive function

1. If stack empty return empty stack
2. If stack not empty
   1. pop character from stack and store it in local variable.
   2. Call the printInOrder function (Before calling this function present state of the calling function will be stored in InBuilt stack)
   3. prints the character(after control comes back i.e., when stack empty, control comes to this point and starts executing)
   4. push the character

Note:

Please refer recursive calls concept.

Java Code:

//Program starts here

import java.io.*;
import java.util.*;
import java.util.Scanner;

class Main {
public static Stack printInOrder(Stack<Character>st)
{
if(st.empty() == false)//when stack not empty
{
Character ch = st.pop();//popping the character
printInOrder(st);//calling recursively
System.out.println(ch);//Printing the characters
st.push(ch);//Pushing the element
}
return st;//At the end returning the stack(After pushing the all characters)
}
public static void main(String[] args)
{
System.out.println("Enter number of characters to be pushed in stack:");
Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
Stack<Character> st = new Stack<Character>();//Stack declaration
for(int i = 0; i < n; i++)
{
char ch = sc.next().charAt(0);//Reading each character
st.push(ch);
}
   System.out.print("Printing the stack values in pushed order: \n");
st = printInOrder(st);//Calling function

System.out.println("Stack top to bottom: \n");
//Checking the order(Validation purpose)
while(st.empty() == false)
{
System.out.println(st.pop());//Printing stack element one by one
}
}
}

//End of the Program

If you have any doubts please feel free to ask.

Thank you. All the best..!