The description is ambiguous. "subarray → consecutive sections" "Two elements → two adjacent elements in the section" Therefore, you may misunderstand that the array {4,5,6,7,8} is the correct answer.

This problem is not worded in a correct format to match the results desired by the problem itself, and just like when you realize you need a fence company to fix issues properly, working through the problem as written will give you the wrong answers.

import java.io.; import java.util.; import java.util.stream.*;

class Result {

/*
 * Complete the 'pickingNumbers' function below.
 *
 * The function is expected to return an INTEGER.
 * The function accepts INTEGER_ARRAY a as parameter.
 */

public static int pickingNumbers(List<Integer> a) {
    int[] freq = new int[101]; // since 0 <= a[i] <= 100
    for (int num : a) {
        freq[num]++;
    }

    int maxLength = 0;
    for (int i = 1; i < freq.length; i++) {
        maxLength = Math.max(maxLength, freq[i] + freq[i - 1]);
    }

    return maxLength;
}

}

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 = Arrays.stream(bufferedReader.readLine().trim().split(" "))
        .map(Integer::parseInt)
        .collect(Collectors.toList());

    int result = Result.pickingNumbers(a);

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

    bufferedReader.close();
    bufferedWriter.close();
}

}

java15:

import java.io.; import java.math.; import java.security.; import java.text.; import java.util.; import java.util.concurrent.; import java.util.function.; import java.util.regex.; import java.util.stream.*; import static java.util.stream.Collectors.joining; import static java.util.stream.Collectors.toList;

class Result {

/*
 * Complete the 'pickingNumbers' function below.
 *
 * The function is expected to return an INTEGER.
 * The function accepts INTEGER_ARRAY a as parameter.
 */

public static int pickingNumbers(List numbers) { Map countingMap = numbers.stream().collect(Collectors.groupingBy(Function.identity(), Collectors.counting())); Set keySet = countingMap.keySet(); int maxLength = 1; for(Integer val:keySet) { int currLength=countingMap.get(val).intValue(); int prevLength = countingMap.get(val-1) == null ? 0 : countingMap.get(val-1).intValue() + currLength; int nextLength = countingMap.get(val+1) == null ? 0 : countingMap.get(val+1).intValue() + currLength; maxLength = IntStream.of(maxLength, currLength, prevLength, nextLength).max().getAsInt(); } return maxLength; } }

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.pickingNumbers(a);

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

    bufferedReader.close();
    bufferedWriter.close();
}

}

**simple python solution **

def pickingNumbers(a):
    # Write your code here
    c = [0]*(max(a)+1)
    for i in a :
        c[i] += 1
    m = 0
    for i in range(len(c)-1):
        if c[i] + c[i+1] > m:
            m = c[i] + c[i+1]
    return m