Java: Move the nth element from the top of the stack to the top

Last update on May 09 2025 12:57:05 (UTC/GMT +8 hours)

17. Move the nth element from the top to the top.

Write a Java program to implement a stack and move the nth element from the top of the stack to the top.

Sample Solution:

Java Code:

import java.util.Scanner;

public class Stack {
  private int[] arr;
  private int top;

  // Constructor to initialize the stack
  public Stack(int size) {
    arr = new int[size];
    top = -1;
  }

  // Method to push an element onto the stack
  public void push(int num) {
    if (top == arr.length - 1) {
      System.out.println("Stack is full");
    } else {
      top++;
      arr[top] = num;
    }
  }

  // Method to pop an element from the stack
  public int pop() {
    if (top == -1) {
      System.out.println("Stack Underflow");
      return -1;
    } else {
      int poppedElement = arr[top];
      top--;
      return poppedElement;
    }
  }

  // Method to get the top element of the stack
  public int peek() {
    if (top == -1) {
      System.out.println("Stack is empty");
      return -1;
    } else {
      return arr[top];
    }
  }

  // Method to check if the stack is empty
  public boolean isEmpty() {
    return top == -1;
  }

  public void moveNthElementToTop(int n) {
    if (n < 1 || n > top + 1) {
      System.out.println("Invalid index");
    } else {
      int element = arr[top - n + 1];
      for (int i = top - n + 1; i < top; i++) {
        arr[i] = arr[i + 1];
      }
      arr[top] = element;
    }
  }

  // Method to display the elements of the stack
  public void display() {
    if (top == -1) {
      System.out.println("Stack is empty");
    } else {
      System.out.print("Stack elements: ");
      for (int i = top; i >= 0; i--) {
        System.out.print(arr[i] + " ");
      }
      System.out.println();
    }
  }

  public static void main(String[] args) {
    System.out.println("Initialize a stack:");
    Stack stack = new Stack(5);
    System.out.println("Input some elements on the stack:");
    stack.push(1);
    stack.push(2);
    stack.push(3);
    stack.push(4);
    stack.push(5);
    stack.display();
    int n = 2;
    System.out.println("\nMove the nth element from the top of the stack to the top, n = " + n);
    stack.moveNthElementToTop(n);
    stack.display();
    n = 3;
    System.out.println("\nMove the nth element from the top of the stack to the top, n = " + n);
    stack.moveNthElementToTop(n);
    stack.display();
    n = 3;
    System.out.println("\nMove the nth element from the top of the stack to the top, n = " + n);
    stack.moveNthElementToTop(n);
    stack.display();
  }
}

Sample Output:

Initialize a stack:
Input some elements on the stack:
Stack elements: 5 4 3 2 1

Move the nth element from the top of the stack to the top, n = 2
Stack elements: 4 5 3 2 1

Move the nth element from the top of the stack to the top, n = 3
Stack elements: 3 4 5 2 1

Move the nth element from the top of the stack to the top, n = 3
Stack elements: 5 3 4 2 1

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to remove the nth element from the top of a stack and then push it back to the top using an auxiliary structure.
• Write a Java program to implement a method that rotates the nth element from the top to the top by performing a series of pop and push operations.
• Write a Java program to recursively move the nth element from the top of a stack to the top while preserving order.
• Write a Java program to combine two stacks to reposition the nth element from the top to the top.

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