Bubble sort using two Stacks

2.3

Prerequisite : Bubble Sort
Write a function that sort an array of integers using stacks and also uses bubble sort paradigm.

Algorithm:

1. Push all elements of array in 1st stack

2. Run a loop for 'n' times(n is size of array)
   having the following :
   2.a. Keep on pushing elements in the 2nd 
        stack till the top of second stack is 
        smaller than element being pushed from 
        1st stack.
   2.b. If the element being pushed is smaller 
        than top of 2nd stack  then swap them
        (as in bubble sort)
   *Do above steps alternatively

TRICKY STEP: Once a stack is empty, then the 
top of the next stack will be the largest 
number so keep it at its position in array 
i.e arr[len-1-i] and then pop it from that 
stack.
// Java program for bubble sort
// using stack

import java.util.Arrays;
import java.util.Stack;

public class Test 
{
    // Method for bubble sort using Stack
    static void bubbleSortStack(int arr[], int n)
    {
        Stack<Integer> s1 = new Stack<>();
        
        // Push all elements of array in 1st stack
        for (int num : arr)
            s1.push(num);       
        
        Stack<Integer> s2 = new Stack<>();
        
        for (int i = 0; i < n; i++) 
        {
            // alternatively
            if (i % 2 == 0)
            {
                while (!s1.isEmpty())
                {
                    int t = s1.pop();
                    
                    if (s2.isEmpty())
                        s2.push(t);                    
                    else 
                    {
                        if (s2.peek() > t)
                        {
                            // swapping
                            int temp = s2.pop();
                            s2.push(t);
                            s2.push(temp);
                        }
                        else
                        {
                            s2.push(t);
                        }
                    }
                }
                
                // tricky step
                arr[n-1-i] = s2.pop();
            }            
            else
            {
                while(!s2.isEmpty())
                {
                    int t = s2.pop();
                    
                    if (s1.isEmpty())
                        s1.push(t);
                    
                    else 
                    {
                        if (s1.peek() > t)
                        {
                            // swapping
                            int temp = s1.pop();
                            
                            s1.push(t);
                            s1.push(temp);
                        }
                        else
                            s1.push(t);
                    }
                }
                
                // tricky step
                arr[n-1-i] = s1.pop();
            }
        }        
        System.out.println(Arrays.toString(arr));
    }
    
    // Driver Method
    public static void main(String[] args) 
    {
        int arr[] = {15, 12, 44, 2, 5, 10};       
        bubbleSortStack(arr, arr.length);
    }
}

Output:

[2, 5, 10, 12, 15, 44]

This article is contributed by Gaurav Miglani and Abhishek Somani . If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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