MaxArraySum.java

import java.io.*;
import java.math.*;
import java.security.*;
import java.text.*;
import java.util.*;
import java.util.concurrent.*;
import java.util.regex.*;

public class Solution {

    static int maxSubsetSum(int[] arr) {

        // O(n) Time, O(1) Space. Keep track of current max, notice that we could add first item or not.
        
        if (arr.length == 0) return 0;
        if (arr.length == 1) return Math.max(0, arr[0]);

        arr[0] = Math.max(0, arr[0]);
        arr[1] = Math.max(arr[0], arr[1]);

        for (int i = 2; i < arr.length; i++) {

            arr[i] = Math.max(arr[i-1], arr[i] + arr[i-2]);
        
        }

        return arr[arr.length - 1];
    }

    private static final Scanner scanner = new Scanner(System.in);

    public static void main(String[] args) throws IOException {
        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));

        int n = scanner.nextInt();
        scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

        int[] arr = new int[n];

        String[] arrItems = scanner.nextLine().split(" ");
        scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

        for (int i = 0; i < n; i++) {
            int arrItem = Integer.parseInt(arrItems[i]);
            arr[i] = arrItem;
        }

        int res = maxSubsetSum(arr);

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

        bufferedWriter.close();

        scanner.close();
    }
}