Publish Your Article Here

Program: HackerRank stack problem - Find maximum element.

Problem Description:

Problem Reference: Maximum Element

You have an empty sequence, and you will be given N queries. Each query is one of these three types:

  • 1 x -Push the element x into the stack.
  • 2 -Delete the element present at the top of the stack.
  • 3 -Print the maximum element in the stack.

Input Format

The first line of input contains an integer, N. The next N lines each contain an above mentioned query. (It is guaranteed that each query is valid.)

Output Format

For each type 3 query, print the maximum element in the stack on a new line.

Sample Input

1 97
1 20
1 26
1 20
1 91

Sample Output


Our Approach

Our approach is pretty straight forward. We will use two stacks here. The first stack is to keeping track of all the elements to perform push and pop (element stack). And the other is for keeping track of the maximum element (maximum elements stack).

When you read the first element, push it onto both of the stacks.

We maintain the maximum elements stack so that the maximum element till now is on the top. Whenever we push an element, it normally goes to the elements stack, but we also push it to the maximum elements stack if, and only if, it is greater than the current maximum element.

Now, when an element is to be deleted, we pop it directly from the elements stack. We also check if that particular element is the maximum element or not. We do so by comparing the value and the index of the popped element with the element on top of the maximum elements stack. If they are equal, we pop that element as well.

Finally, to answer the maximum element query 3, we print the element on top of the maximum elements stack.

package com.java2novice.algos;

import java.util.Scanner;
import java.util.Stack;

public class StackMaxElement {

    public static void main(String arg[]) {

        Stack<Integer> stack = new Stack<>();
        Stack<Integer> maxStack = new Stack<>();

        Scanner snr = new Scanner(;
        int n = snr.nextInt();
        for(int i=0;i<n;i++) {
            int input = snr.nextInt();
            switch (input){
                case 1:
                    int x = snr.nextInt();
                    if(maxStack.isEmpty() || x >= maxStack.peek()) {

                case 2:
                    int popVl = stack.pop();
                    if(popVl == maxStack.peek()) {

                case 3:

                default: break;

---User Input---
1 97
1 20
1 26
1 20
1 91
---Program Output---

<< Previous Program | Next Program >>

List Of All Interview Programs:

  1. Remove last node of the Linked List
  2. Identify middle element of a Linked List
  3. Identify given LinkedList is a palindrom or not using Stack.
  4. Remove duplicates from sorted linked list
  5. Find Nth node from the end of Linked List
  6. Identify loop/cycle in a LinkedList.
  7. Find length of a loop in a LinkedList.
  8. Detect and remove loop in a LinkedList.
  9. How to reverse Singly Linked List?
  10. Check if given Linked List is a Circular Linked List or not.
  11. Find out duplicate number between 1 to N numbers.
  12. Find out middle index where sum of both ends are equal.
  13. Write a singleton class.
  14. Write a program to create deadlock between two threads.
  15. Write a program to reverse a string using recursive algorithm.
  16. Write a program to reverse a number.
  17. Write a program to convert decimal number to binary format.
  18. Write a program to find perfect number or not.
  19. Write a program to implement ArrayList.
  20. Write a program to find maximum repeated words from a file.
  21. Wrie a program to find out duplicate characters in a string.
  22. Write a program to find top two maximum numbers in a array.
  23. Write a program to sort a map by value.
  24. Write a program to find common elements between two arrays.
  25. How to swap two numbers without using temporary variable?
  26. Write a program to print fibonacci series.
  27. Write a program to find sum of each digit in the given number using recursion.
  28. Write a program to check the given number is a prime number or not?
  29. Write a program to find the given number is Armstrong number or not?
  30. Write a program to convert binary to decimal number.
  31. Write a program to check the given number is binary number or not?
  32. Write a program for Bubble Sort in java.
  33. Write a program for Insertion Sort in java.
  34. Write a program to implement hashcode and equals.
  35. How to get distinct elements from an array by avoiding duplicate elements?
  36. Write a program to get distinct word list from the given file.
  37. Write a program to get a line with max word count from the given file.
  38. Write a program to convert string to number without using Integer.parseInt() method.
  39. Write a program to find two lines with max characters in descending order.
  40. Write a program to find the sum of the first 1000 prime numbers.
  41. Find longest substring without repeating characters.
  42. Write a program to remove duplicates from sorted array.
  43. How to sort a Stack using a temporary Stack?
  44. Write a program to print all permutations of a given string.
  45. Implement Binary Search Tree (BST)
  46. Find min and max value from Binary Search Tree (BST)
  47. Find height of a Binary Search Tree (BST)
  48. Implement Binary Search Tree (BST) Level order traversal (breadth first).
  49. Implement Binary Search Tree (BST) pre-order traversal (depth first).
  50. Implement Binary Search Tree (BST) in-order traversal (depth first).
  51. Implement Binary Search Tree (BST) post-order traversal (depth first).
  52. How to check the given Binary Tree is Binary Search Tree (BST) or not?
  53. How to delete a node from Binary Search Tree (BST)?
  54. Write a program to find common integers between two sorted arrays.
  55. Write a program to find given two trees are mirror or not.
  56. HackerRank stack problem - Find maximum element.
  57. HackerRank stack problem - Balanced Brackets.
  58. HackerRank stack problem - Equal Stacks.
  59. HackerRank stack problem - Game Of Two Stacks.
Knowledge Centre
Preemptive scheduling Vs Time slicing?
Preemptive scheduling: The highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence.

Time slicing: A task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.
Famous Quotations
Discipline is just choosing between what you want now and what you want most.
-- Unknown Author

About Author

I'm Nataraja Gootooru, programmer by profession and passionate about technologies. All examples given here are as simple as possible to help beginners. The source code is compiled and tested in my dev environment.

If you come across any mistakes or bugs, please email me to [email protected].

Most Visited Pages

Other Interesting Sites

Reference: Java™ Platform Standard Ed. 7 - API Specification | Java™ Platform Standard Ed. 8 - API Specification | Java is registered trademark of Oracle.
Privacy Policy | Copyright © 2024 by Nataraja Gootooru. All Rights Reserved.