Code Challenge 11/15/2013

recursion.java

// A utility method that finds the sum of numbers at odd indexes within a sub-
	// array starting with startIndex and ending at endIndex
	public static int computeSumAtOdd(int[] numbers, int startIndex, int endIndex)
	{
		if (startIndex == endIndex) // base case: array of size 1, returns number if index odd
		{
			if (startIndex%2 == 1)
				return numbers[startIndex];
			else
				return 0;
		}
		else // recursion: return the sum of odd-index numbers in right half and left half
		{
			int midIndex = (startIndex + endIndex)/2;
			int leftSumAtOdd = computeSumAtOdd(numbers, startIndex, midIndex);
			int rightSumAtOdd = computeSumAtOdd(numbers, midIndex+1, endIndex);
			return leftSumAtOdd + rightSumAtOdd;
		}
	}