Part-II : Stream API Coding Questions

Created on: Sep 18, 2024

Stream api

Partition a array into two parts based on even and odd.

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9);
Map<Boolean, List<Integer>> evenOddPartition =  numbers.stream()
        .collect(Collectors.partitioningBy(n->n%2==0));
System.out.println(evenOddPartition);

{false=[1, 3, 5, 7, 9], true=[2, 4, 6, 8]}

Find the longest string in a list of strings using Java streams ?

List<String> strings = Arrays
              .asList("apple", "banana", "cherry", "date", "grapefruit");

String longestString = strings.stream()
        .max(Comparator.comparingInt(String::length)).get();
System.out.println(longestString);

grapefruit

Check if a array contains any prime number of not.

import java.util.List;
import java.util.Arrays;
public class Query {
    public static boolean isPrime(int number) {
        for (int i = 2; i < number / 2; i++) {
            if (number % i == 0)
                return false;
        }
        return true;
    }

    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(29, 15, 11, 6, 13, 22, 19, 17, 21, 7);
        boolean primeNumberPresent = numbers.stream()
                .anyMatch(Query::isPrime);
        System.out.println(primeNumberPresent);
    }
}

true

Find the occurrence of each word on the array.

String[] words= {"apple", "banana", "apple", "orange", "banana", "apple"};
Map<String, Long> wordCount = Arrays.asList(words)
        .stream().collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
System.out.println(wordCount);

{orange=1, banana=2, apple=3}

Function.identity: Returns a function that always returns its input argument.

Remove duplicate from array and arrange in descending order.

List<Integer> numbers = Arrays.asList(1, 2, 3, 2, 4, 5, 1);
List<Integer> distinctNum = numbers.stream().distinct()
        .sorted(Comparator.comparingInt(Integer::intValue).reversed())
        .collect(Collectors.toList());
System.out.println(distinctNum);

[5, 4, 3, 2, 1]

Given two array in sorted order, merge them in sorted order.

List<Integer> list1 = Arrays.asList(0, 3, 5, 7, 10);
List<Integer> list2 = Arrays.asList(2, 4, 6, 9, 11);
List<Integer> res = Stream.concat(list1.stream(), list2.stream())
        .sorted().collect(Collectors.toList());
System.out.println(res);

[0, 2, 3, 4, 5, 6, 7, 9, 10, 11]

Given two array, find the common item between them,

List<Integer> list1 = Arrays.asList(1, 2, 3, 4, 5);
List<Integer> list2 = Arrays.asList(3, 4, 5, 6, 7);
List<Integer> common = list1.stream()
        .filter(list2::contains)
        .collect(Collectors.toList());
System.out.println(common);

[3, 4, 5]

Find the average of item in array of type double.

List<Double> doubles = Arrays.asList(6.5, 7.3, 8.9, 9.1, 10.2, 11.4, 12.6, 13.7, 14.5, 15.3);

OptionalDouble average = doubles.stream().mapToDouble(Double::doubleValue).average();
System.out.println(average);
``
```less
OptionalDouble[10.95]

Find kth smallest element in array.

int[] array = {20, 35, 15, 40, 5, 25, 30, 10, 50, 45};
int k = 4;

int kthSmallest=  Arrays.stream(array).sorted().skip(k-1).findFirst().orElse(-1);
System.out.println(kthSmallest);

Concatenate string with space in between the string.

String[] arr = {"How", "are", "you"};
String finalStr =  Arrays.stream(arr).collect(Collectors.joining(" "));
System.out.println(finalStr);

How are you

Given a list of integers, find the product of all non-negative integers.

List<Integer> list = Arrays.asList(4, 5, -6, 7, -1, 2, -3);

long res = list.stream().filter(n -> n < 0).mapToLong(Integer::longValue).reduce(1, (a, b) -> a * b);
System.out.println(res);

-18

Given a list of string, find the longest palindrome string.

List<String> list = List.of("racecar", "apple", "civic", "rotator", "banana", "deified", "python", "noon", "kayak", "developer");

String longestPalindrom = list.stream()
        .filter(s -> new StringBuilder(s).reverse().toString().equalsIgnoreCase(s))
        .max(Comparator.comparingInt(String::length)).get();
System.out.println(longestPalindrom);

racecar

Given a list of string, find the string which starts with vowel.

List<String> fruits = Arrays.asList("Litchi", "apple", "mango", "pomegranate", "banana", "orange", "kiwi", "strawberry");

List<String> fruitWithVowelFirst = fruits.stream().filter(s -> "aeiou".contains(String.valueOf(s.charAt(0))))
        .collect(Collectors.toList());
System.out.println(fruitWithVowelFirst);

[apple, orange]