# Java Array: Exercises, Practice, Solution

## Java Array Exercises [79 exercises with solution]

**1.** Write a Java program to sort a numeric array and a string array. Go to the editor

**2.** Write a Java program to sum values of an array. Go to the editor

**3.** Write a Java program to print the following grid. Go to the editor

Expected Output :

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

**4.** Write a Java program to calculate the average value of array elements. Go to the editor

**5.** Write a Java program to test if an array contains a specific value. Go to the editor

**6.** Write a Java program to find the index of an array element. Go to the editor

**7.** Write a Java program to remove a specific element from an array. Go to the editor

**8.** Write a Java program to copy an array by iterating the array. Go to the editor

**9.** Write a Java program to insert an element (specific position) into an array. Go to the editor

**10.** Write a Java program to find the maximum and minimum value of an array. Go to the editor

**11.** Write a Java program to reverse an array of integer values. Go to the editor

**12.** Write a Java program to find the duplicate values of an array of integer values. Go to the editor

**13.** Write a Java program to find the duplicate values of an array of string values. Go to the editor

**14.** Write a Java program to find the common elements between two arrays (string values). Go to the editor

**15.** Write a Java program to find the common elements between two arrays of integers. Go to the editor

**16.** Write a Java program to remove duplicate elements from an array. Go to the editor

**17.** Write a Java program to find the second largest element in an array. Go to the editor

**18.** Write a Java program to find the second smallest element in an array. Go to the editor

**19.** Write a Java program to add two matrices of the same size. Go to the editor

**20.** Write a Java program to convert an array to ArrayList. Go to the editor

**21.** Write a Java program to convert an ArrayList to an array. Go to the editor

**22.** Write a Java program to find all pairs of elements in an array whose sum is equal to a specified number. Go to the editor

**23.** Write a Java program to test the equality of two arrays. Go to the editor

**24.** Write a Java program to find a missing number in an array. Go to the editor

**25.** Write a Java program to find common elements from three sorted (in non-decreasing order) arrays. Go to the editor

**26.** Write a Java program to move all 0's to the end of an array. Maintain the relative order of the other (non-zero) array elements. Go to the editor

**27.** Write a Java program to find the number of even and odd integers in a given array of integers. Go to the editor

**28.** Write a Java program to get the difference between the largest and smallest values in an array of integers. The length of the array must be 1 and above. Go to the editor

**29.** Write a Java program to compute the average value of an array of integers except the largest and smallest values. Go to the editor

**30.** Write a Java program to check if an array of integers without 0 and -1. Go to the editor

**31.** Write a Java program to check if the sum of all the 10's in the array is exactly 30. Return false if the condition does not satisfy, otherwise true. Go to the editor

**32.** Write a Java program to check if an array of integers contains two specified elements 65 and 77. Go to the editor

**33.** Write a Java program to remove the duplicate elements of a given array and return the new length of the array.

Sample array: [20, 20, 30, 40, 50, 50, 50]

After removing the duplicate elements the program should return 4 as the new length of the array. Go to the editor

**34.** Write a Java program to find the length of the longest consecutive elements sequence from a given unsorted array of integers.

Sample array: [49, 1, 3, 200, 2, 4, 70, 5]

The longest consecutive elements sequence is [1, 2, 3, 4, 5], therefore the program will return its length 5. Go to the editor

**35.** Write a Java program to find the sum of the two elements of a given array which is equal to a given integer.

Sample array: [1,2,4,5,6]

Target value: 6. Go to the editor

**36.** Write a Java program to find all the unique triplets such that sum of all the three elements [x, y, z (x ≤ y ≤ z)] equal to a specified number.

Sample array: [1, -2, 0, 5, -1, -4]

Target value: 2. Go to the editor

**37.** Write a Java program to create an array of its anti-diagonals from a given square matrix. Go to the editor

Example:

Input :

1 2

3 4

Output:

[

[1],

[2, 3],

[4]

]

**38.** Write a Java program to get the majority element from a given array of integers containing duplicates. Go to the editor

Majority element: A majority element is an element that appears more than n/2 times where n is the size of the array.

**39.** Write a Java program to print all the LEADERS in the array. Go to the editor

Note: An element is leader if it is greater than all the elements to its right side.

**40.** Write a Java program to find the two elements from a given array of positive and negative numbers such that their sum is closest to zero. Go to the editor

**41.** Write a Java program to find smallest and second smallest elements of a given array. Go to the editor

**42.** Write a Java program to segregate all 0s on left side and all 1s on right side of a given array of 0s and 1s. Go to the editor

**43.** Write a Java program to find all combination of four elements of a given array whose sum is equal to a given value. Go to the editor

**44.** Write a Java program to count the number of possible triangles from a given unsorted array of positive integers. Go to the editor

Note: The triangle inequality states that the sum of the lengths of any two sides of a triangle must be greater than or equal to the length of the third side.

**45.** Write a Java program to cyclically rotate a given array clockwise by one. Go to the editor

**46.** Write a Java program to check whether there is a pair with a specified sum of a given sorted and rotated array. Go to the editor

**47.** Write a Java program to find the rotation count in a given rotated sorted array of integers. Go to the editor

**48.** Write a Java program to arrange the elements of a given array of integers where all negative integers appear before all the positive integers. Go to the editor

**49.** Write a Java program to arrange the elements of a given array of integers where all positive integers appear before all the negative integers. Go to the editor

**50.** Write a Java program to sort an array of positive integers of a given array, in the sorted array the value of the first element should be maximum, second value should be minimum value, third should be second maximum, fourth second be second minimum and so on. Go to the editor

**51.** Write a Java program to separate 0s on left side and 1s on right side of an array of 0s and 1s in random order. Go to the editor

**52.** Write a Java program to separate even and odd numbers of a given array of integers. Put all even numbers first, and then odd numbers. Go to the editor

**53.** Write a Java program to replace every element with the next greatest element (from right side) in a given array of integers. There is no element next to the last element, therefore replace it with -1. Go to the editor

**54.** Write a Java program to check if a given array contains a subarray with 0 sum. Go to the editor

Example:

Input :

nums1= { 1, 2, -2, 3, 4, 5, 6 }

nums2 = { 1, 2, 3, 4, 5, 6 }

nums3 = { 1, 2, -3, 4, 5, 6 }

Output:

Does the said array contain a subarray with 0 sum: true

Does the said array contain a subarray with 0 sum: false

Does the said array contain a subarray with 0 sum: true

**55.** Write a Java program to print all sub-arrays with 0 sum present in a given array of integers. Go to the editor

Example:

Input :

nums1 = { 1, 3, -7, 3, 2, 3, 1, -3, -2, -2 }

nums2 = { 1, 2, -3, 4, 5, 6 }

nums3= { 1, 2, -2, 3, 4, 5, 6 }

Output:

Sub-arrays with 0 sum : [1, 3, -7, 3]

Sub-arrays with 0 sum : [3, -7, 3, 2, 3, 1, -3, -2]

Sub-arrays with 0 sum : [1, 2, -3]

Sub-arrays with 0 sum : [2, -2]

**56.** Write a Java program to sort a given binary array in linear times. Go to the editor

From Wikipedia,

Linear time: An algorithm is said to take linear time, or O(n) time, if its time complexity is O(n). Informally, this means that the running time increases at most linearly with the size of the input. More precisely, this means that there is a constant c such that the running time is at most cn for every input of size n. For example, a procedure that adds up all elements of a list requires time proportional to the length of the list, if the adding time is constant, or, at least, bounded by a constant.

Linear time is the best possible time complexity in situations where the algorithm has to sequentially read its entire input. Therefore, much research has been invested into discovering algorithms exhibiting linear time or, at least, nearly linear time. This research includes both software and hardware methods. There are several hardware technologies which exploit parallelism to provide this. An example is content-addressable memory. This concept of linear time is used in string matching algorithms such as the Boyer–Moore algorithm and Ukkonen's algorithm.

Example:

Input :

b_nums[] = { 0, 1, 1, 0, 1, 1, 0, 1, 0, 0 }

Output:

After sorting: [0, 0, 0, 0, 0, 1, 1, 1, 1, 1]

**57.** Write a Java program to check if a sub-array is formed by consecutive integers from a given array of integers. Go to the editor

Example:

Input :

nums = { 2, 5, 0, 2, 1, 4, 3, 6, 1, 0 }

Output:

The largest sub-array is [1, 7]

Elements of the sub-array: 5 0 2 1 4 3 6

**58.** Given two sorted arrays A and B of size p and q, write a Java program to merge elements of A with B by maintaining the sorted order i.e. fill A with first p smallest elements and fill B with remaining elements. Go to the editor

Example:

Input :

int[] A = { 1, 5, 6, 7, 8, 10 }

int[] B = { 2, 4, 9 }

Output:

Sorted Arrays:

A: [1, 2, 4, 5, 6, 7]

B: [8, 9, 10]

**59.** Write a Java program to find maximum product of two integers in a given array of integers. Go to the editor

Example:

Input :

nums = { 2, 3, 5, 7, -7, 5, 8, -5 }

Output:

Pair is (7, 8), Maximum Product: 56

**60.** Write a Java program to shuffle a given array of integers. Go to the editor

Example:

Input :

nums = { 1, 2, 3, 4, 5, 6 }

Output:

Shuffle Array: [4, 2, 6, 5, 1, 3]

**61.** Write a Java program to rearrange a given array of unique elements such that every second element of the array is greater than its left and right elements. Go to the editor

Example:

Input :

nums= { 1, 2, 4, 9, 5, 3, 8, 7, 10, 12, 14 }

Output:

Array with every second element is greater than its left and right elements:

[1, 4, 2, 9, 3, 8, 5, 10, 7, 14, 12]

**62.** Write a Java program to find the equilibrium indices from a given array of integers. Go to the editor

Example:

Input :

nums = {-7, 1, 5, 2, -4, 3, 0}

Output:

Equilibrium indices found at : 3

Equilibrium indices found at : 6

**63.** Write a Java program to replace each element of the array with product of every other element in a given array of integers. Go to the editor

Example:

Input :

nums1 = { 1, 2, 3, 4, 5, 6, 7}

nums2 = {0, 1, 2, 3, 4, 5, 6, 7}

Output:

Array with product of every other element:

[5040, 2520, 1680, 1260, 1008, 840, 720]

Array with product of every other element:

[5040, 0, 0, 0, 0, 0, 0, 0]

**64.** Write a Java program to find Longest Bitonic Subarray in a given array. Go to the editor

A bitonic subarray is a subarray of a given array where elements are first sorted in increasing order, then in decreasing order. A strictly increasing or strictly decreasing subarray is also accepted as bitonic subarray.

Example:

Input :

nums = { 4, 5, 9, 5, 6, 10, 11, 9, 6, 4, 5 }

Output:

The longest bitonic subarray is [3,9]

Elements of the said sub-array: 5 6 10 11 9 6 4

The length of longest bitonic subarray is 7

**65.** Write a Java program to find maximum difference between two elements in a given array of integers such that smaller element appears before larger element. Go to the editor

Example:

Input :

nums = { 2, 3, 1, 7, 9, 5, 11, 3, 5 }

Output:

The maximum difference between two elements of the said array elements

10

**66.** Write a Java program to find contiguous subarray within a given array of integers which has the largest sum. Go to the editor

In computer science, the maximum sum subarray problem is the task of finding a contiguous subarray with the largest sum, within a given one-dimensional array A[1...n] of numbers. Formally, the task is to find indices and with, such that the sum is as large as possible.

Example:

Input :

int[] A = {1, 2, -3, -4, 0, 6, 7, 8, 9}

Output:

The largest sum of contiguous sub-array: 30

**67.** Write a Java program to find subarray which has the largest sum in a given circular array of integers. Go to the editor

Example:

Input :

nums1 = { 2, 1, -5, 4, -3, 1, -3, 4, -1 }

nums2 = { 1, -2, 3, 0, 7, 8, 1, 2, -3 }

Output:

The sum of subarray with the largest sum is 6

The sum of subarray with the largest sum is 21

**68.** Write a Java program to create all possible permutations of a given array of distinct integers. Go to the editor

Example:

Input :

nums1 = {1, 2, 3, 4}

nums2 = {1, 2, 3}

Output:

Possible permutations of the said array:

[1, 2, 3, 4]

[1, 2, 4, 3]

....

[4, 1, 3, 2]

[4, 1, 2, 3]

Possible permutations of the said array:

[1, 2, 3]

[1, 3, 2]

...

[3, 2, 1]

[3, 1, 2]

**69.** Write a Java program to find minimum subarray sum of specified size in a given array of integers. Go to the editor

Example:

Input :

nums = { 1, 2, 3, 4, 5, 6, 7, 8, 9,10}

Output:

Sub-array size: 4

Sub-array from 0 to 3 and sum is: 10

**70.** Write a Java program to find the smallest length of a contiguous subarray of which the sum is greater than or equal to specified value. Return 0 instead. Go to the editor

Example:

Input :

nums = {1, 2, 3, 4, 6}

Output:

Minimum length of a contiguous subarray of which the sum is 8, 2

**71.** Write a Java program to form the largest number from a given list of non negative integers. Go to the editor

Example:

Input :

nums = {1, 2, 3, 0, 4, 6}

Output:

Largest number using the said array numbers: 643210

**72.** Write a Java program to find and print one continuous subarray (from a given array of integers) that if you only sort the said subarray in ascending order then the entire array will be sorted in ascending order. Go to the editor

Example:

Input :

nums1 = {1, 2, 3, 0, 4, 6}

nums2 = { 1, 3, 2, 7, 5, 6, 4, 8}

Output:

Continuous subarray:

1 2 3 0

Continuous subarray:

3 2 7 5 6 4

**73.** Write a Java program to sort a given array of distinct integers where all its numbers are sorted except two numbers. Go to the editor

Example:

Input :

nums1 = { 3, 5, 6, 9, 8, 7 }

nums2 = { 5, 0, 1, 2, 3, 4, -2 }

Output:

After sorting new array becomes: [3, 5, 6, 7, 8, 9]

After sorting new array becomes: [-2, 0, 1, 2, 3, 4, 5]

**74.** Write a Java program to find all triplets equal to a given sum in a unsorted array of integers. Go to the editor

Example:

Input :

nums = { 1, 6, 3, 0, 8, 4, 1, 7 }

Output:

Triplets of sum 7

(0 1 6)

(0 3 4)

**75.** Write a Java program to calculate the largest gap between sorted elements of an array of integers. Go to the editor

Example:

Original array: [23, -2, 45, 38, 12, 4, 6]

Largest gap between sorted elements of the said array: 15

**76.** Write a Java program to determine whether numbers in an array can be rearranged so that each number appears exactly once in a consecutive list of numbers. Return true otherwise false. Go to the editor

Example:

Original array: [1, 2, 5, 0, 4, 3, 6]

Check consecutive numbers in the said array!true

**77.** Write a Java program that checks whether an array of integers alternates between positive and negative values. Go to the editor

Example:

Original array: [1, -2, 5, -4, 3, -6]

Check the said array of integers alternates between positive and negative values!true

**78.** Write a Java program that checks an array is negative dominant or not. If the array is negative dominant return true otherwise false. Go to the editor

Example:

Original array of numbers:

[1, -2, -5, -4, 3, -6]

Check Negative Dominance in the said array!true

**79.** Write a Java program that returns the missing letter from an array of increasing letters (upper or lower). Assume there will always be one letter missing in the array. Go to the editor

Example:

Original array of elements:

[p, r, s, t]

Missing letter in the said array: q

## Java Code Editor:

**More to Come !**

**Do not submit any solution of the above exercises at here, if you want to contribute go to the appropriate exercise page.**

## Java: Tips of the Day

**everyNth:**

Returns every nth element in an array.

Use IntStream.range().filter() to create a new array that contains every nth element of a given array.

public static int[] everyNth(int[] elements, int nth) { return IntStream.range(0, elements.length) .filter(i -> i % nth == nth - 1) .map(i -> elements[i]) .toArray(); }

Ref: https://bit.ly/3CBWdji

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