## Queue using Two Stacks – Java Code & Algorithm

How to implement a queue using two stacks. In this tutorial, We are going to discuss an algorithm and java code to implement a queue using two stacks.

## Find Common Elements in Three Sorted Arrays – Java Code

Write a java program to find common elements in three sorted arrays. Given three sorted arrays, write a code to print intersection of three sorted arrays.

For example –

arr1 = {1, 5, 10, 20, 40, 80};
arr2 = {6, 7, 20, 80, 100};
arr3 = {3, 4, 15, 20, 30, 70, 80, 120};

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Output : {20, 80}

20 and 80 is the common element between three sorted arrays.

## Get Minimum Element from Stack in O(1)

Design a stack to get minimum element from stack in O(1) (constant time).

For example : Suppose, If we push following elements in a stack.

9  ==> Top
1
2
3

Then if we call getMin() method, It will return 1 in O(1) (constant time). In a stack, Element which pushed last in the stack is the first element to be popped out. Think for a moment how we can solve this problem.

## Find Middle Element of a Linked List – Java Code

In this tutorial, We are going to explain how to find middle element of a linked list in Java. This programming question is mostly asked in a technical interviews.

For example: Given a linked list, the middle element in this linked list is 8.

15 -> 9 -> 8 -> 5 -> 6 -> NULL

There are multiple approaches to solve this problem. In this tutorial, We are going to learn two approaches through which we can find middle element of a singly linked list. Also, i have also added video tutorial at the end of this tutorial.

## Java Program to Reverse a String using Stack

Write a java program to reverse a string using stack data structure. Given an input string, We have to write a java code to reverse a string using stack.

In my previous tutorial, I have explained java program to reverse a string using recursion.

Before solving this problem, Let’s understand what is a stack data structure.

## Find Pairs with Given Sum in a Sorted Array – Java Code

Java code to find pairs with given sum in a sorted array. Given an array A of size N. Write a java code to find all pairs in the array that sum to a number equal to K. If no such pair exists then output will be 1.  Array elements are distinct and in a sorted order.

For example –

Input :

arr[] = {1, 2, 3, 4, 5, 6, 7};
sum = 9

Output:

Pairs with given sum 9 is

Pair (2 , 7 )
Pair (3 , 6 )
Pair (4 , 5 )

## Segregate 0s and 1s in an Array – Java Code

Segregate 0s and 1s in an Array. Given an array of 0s and 1s in random order. Write a java program to segregate 0’s on left side and 1’s on right side of the array.

For example –

Input array = [0, 1, 0, 1, 0, 0, 1]
Output array = [0, 0, 0, 0, 1, 1, 1]

## Find First and Last Position of a Number in a Sorted Array – Java Code

Given a sorted array which contains duplicate elements, Write a java code to find first and last position of a number in a sorted array. Given a number x, write a code to find it’s first and last index in an array.

For example –

Suppose the input array is arr[] : {1, 4, 7, 8, 8, 11, 11, 11, 11, 12, 13, 13} and the number to be searched is 11. Then the first index of 11 is 5 and last index is 8.

## Find Intersection of Two Arrays – Java Code

Given two sorted arrays, Write a java code to find intersection of two arrays.

For example, if the input arrays are:

arr1[] = {2, 3, 6, 7, 9, 11}
arr2[] = {4, 6, 8, 9, 12}

Then your program should print intersection as {6, 9}. Before writing actual code, let’s first discuss different approaches to solve this problem.

## Move All Zeroes to End of Array – Java Code

Write a java program to move all zeroes to end of array. Given an array of random integers move all zeroes to end of array. The order of all other elements of an array should be same.

In this tutorial, We are going to discuss and write a java program to move zeroes to end of an array. It is another interesting problem which generally asked in a technical interviews.

For example –

Input : {1, 2, 0, 4, 0, 5, 3, 8}

Output: {1, 2, 4, 5, 3, 8, 0, 0}

You can see in the example, we have moved zeroes to the end of an array.