public class MaxThreeConsecutiveSum {
/**
* Stores the result of the search.
*/
public static class Result {
private final int startIndex;
private final int maxSum;
public Result(int startIndex, int maxSum) {
this.startIndex = startIndex;
this.maxSum = maxSum;
}
public int getStartIndex() {
return startIndex;
}
public int getMaxSum() {
return maxSum;
}
}
/**
* Finds three consecutive numbers with the largest sum.
*
* @param numbers Input array
* @return Result containing:
* - start index of the best sequence
* - largest sum found
* @throws IllegalArgumentException if the array has fewer than 3 elements
*/
public static Result findMaxSumOfThree(int[] numbers, int total) {
if (numbers == null || numbers.length < total) {
throw new IllegalArgumentException(
"Array must contain at least " + total + " elements."
);
}
// Sum of the first window
int currentSum = numbers[0] + numbers[1] + numbers[2];
int maxSum = currentSum;
int bestIndex = 0;
// Slide the window across the array
for (int i = 3; i < numbers.length; i++) {
// Add new element and remove old element
currentSum += numbers[i];
currentSum -= numbers[i - total];
if (currentSum > maxSum) {
maxSum = currentSum;
bestIndex = i - 2;
}
}
return new Result(bestIndex, maxSum);
}
public static void main(String[] args) {
int[] numbers = {4, 2, 7, 1, 8, 3, 9};
Result result = findMaxSumOfThree(numbers, 3);
System.out.println("Largest sum: " + result.getMaxSum());
System.out.println(
"Numbers: "
+ numbers[result.getStartIndex()] + " "
+ numbers[result.getStartIndex() + 1] + " "
+ numbers[result.getStartIndex() + 2]
);
}
}
/*
run:
Largest sum: 20
Numbers: 8 3 9
*/
