Lonely Integer Hackerrank solution in Java | Find unique element in Java Array

Find unique elements from given Array in Java with Explanation | Lonely Integer Hackerrank solution 

Problem Description :

Given an array of integers, where all elements but one occur twice, find the unique element. 

Example :

array = [1, 2, 3, 4, 3, 2, 1]
The unique element is 4.

So we have given array, in which all elements occurs twice but 1 elements only occurs once and we have to find that unique element.

Solution 1 : Find unique element from Java array

    import java.io.*;

    import java.util.*;

    import java.util.stream.*;

    import static java.util.stream.Collectors.toList;

    class Result {

        public static int lonelyinteger(List<Integer> a) {

            

            Map<Integer, Integer> map = new HashMap<>();

            for (Integer elem : a) {

                if (!map.containsKey(elem)) {

                    map.put(elem, 1);

                } else {

                    map.put(elem, map.get(elem)+1);

                }

            }

            

            for (Map.Entry<Integer, Integer> entry : map.entrySet()) {

                if (entry.getValue() == 1) {

                    return entry.getKey();

                }

        

            }

            return 0;

        }

    }

    public class Solution {

        public static void main(String[] args) throws IOException {

            BufferedReader bufferedReader = new BufferedReader(

                new InputStreamReader(System.in));

            BufferedWriter bufferedWriter = new BufferedWriter(

                new FileWriter(System.getenv("OUTPUT_PATH")));

            int n = Integer.parseInt(bufferedReader.readLine().trim());

            List<Integer> a = Stream.of(bufferedReader.readLine()

                .replaceAll("\\s+$", "").split(" "))

                .map(Integer::parseInt)

                .collect(toList());

            int result = Result.lonelyinteger(a);

            bufferedWriter.write(String.valueOf(result));

            bufferedWriter.newLine();

            bufferedReader.close();

            bufferedWriter.close();

        }

    }

Solution explanation :

• Here we are using Map for find solution of Lonely Integer problem.
• In first foreach loop, store all List elements and its occurrence in map. Like [1=2, 2=2, 3=2, 4=1]
• Using this approach, map contains all elements and its occurrence value.
• In second foreach loop, iterate through Map and return Key whoever Value contains 1. Means unique element.

 

Happy coding. Happy learning.

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