Reverse Stack Using Recursion Algorithm
The Reverse Stack Using Recursion Algorithm is an efficient technique to reverse the order of elements in a stack data structure by utilizing the concept of recursion. A stack is a linear data structure that follows the Last In First Out (LIFO) principle, meaning that the last element added to the stack is the first one to be removed. In this algorithm, instead of using another stack or any data structure to store the elements, the function calls itself recursively to reverse the order of items in the stack. This algorithm is particularly useful when the goal is to reverse a stack without using any additional memory or data structures.
The algorithm can be implemented in two main steps. First, the base case checks whether the stack is empty or has only one element. If either condition is true, the algorithm returns without making any changes. However, if there are multiple elements, the algorithm removes the top element from the stack and makes a recursive call to the reverse function with the remaining stack. After the recursive call, a separate helper function is used to insert the removed element at the bottom of the stack. This helper function also uses recursion, as it first removes all the elements above the desired position, then inserts the target element and restores the elements above it. As the Reverse Stack Using Recursion Algorithm continues to call itself with the updated stacks, it eventually reverses the order of all elements in the original stack.
package Others;
/* Program to reverse a Stack using Recursion*/
import java.util.Stack;
public class ReverseStackUsingRecursion {
//Stack
private static Stack<Integer> stack = new Stack<>();
//Main function
public static void main(String[] args) {
//To Create a Dummy Stack containing integers from 0-9
for (int i = 0; i < 10; i++) {
stack.push(i);
}
System.out.println("STACK");
//To print that dummy Stack
for (int k = 9; k >= 0; k--) {
System.out.println(k);
}
//Reverse Function called
reverseUsingRecursion(stack);
System.out.println("REVERSED STACK : ");
//To print reversed stack
while (!stack.isEmpty()) {
System.out.println(stack.pop());
}
}
//Function Used to reverse Stack Using Recursion
private static void reverseUsingRecursion(Stack<Integer> stack) {
if (stack.isEmpty()) // If stack is empty then return
{
return;
}
/* All items are stored in call stack until we reach the end*/
int temptop = stack.peek();
stack.pop();
reverseUsingRecursion(stack); //Recursion call
insertAtEnd(temptop); // Insert items held in call stack one by one into stack
}
//Function used to insert element at the end of stack
private static void insertAtEnd(int temptop) {
if (stack.isEmpty()) {
stack.push(temptop); // If stack is empty push the element
} else {
int temp = stack.peek(); /* All the items are stored in call stack until we reach end*/
stack.pop();
insertAtEnd(temptop); //Recursive call
stack.push(temp);
}
}
}
