ReverseStack.java

package RecursionAndBacktracking;
/*
* Reverse stack using recursion without using extra space.
*/
import java.util.Scanner;
import java.util.Stack;

public class ReverseStack {
 private static void reverseStack(Stack<Integer> stack){
 // Base Condition
 if(stack.size() == 1)
 return;
 int val = stack.pop();
 reverseStack(stack);
 pushValAtEnd(stack, val);
 }
 public static void pushValAtEnd(Stack<Integer> stack, int val){
 // Base condition
 if(stack.size() == 0){
 stack.push(val);
 return;
 }
 int temp = stack.pop();
 pushValAtEnd(stack, val);
 stack.push(temp);
 }
 public static void main(String[] args) {
 Scanner sc = new Scanner(System.in);
 System.out.println("Enter the number of test cases:");
 int t = sc.nextInt();

 while (t-- > 0) {
 System.out.println("Enter elements: if want to stop enter -1");
 Stack<Integer> stack = new Stack<>();
 int ele = 0;
 ele = sc.nextInt();
 while (ele != -1){
 stack.push(ele);
 ele = sc.nextInt();
 }
 reverseStack(stack);
 System.out.println(stack);
 }
 }
}