smallestSubArraySum.java

class MinSizeSubArraySum {
  public static int findMinSubArray(int S, int[] arr) {
    int windowSum = 0, minLength = Integer.MAX_VALUE;
    int windowStart = 0;
    for (int windowEnd = 0; windowEnd < arr.length; windowEnd++) {
      windowSum += arr[windowEnd]; // add the next element
      // shrink the window as small as possible until the 'windowSum' is smaller than 'S'
      while (windowSum >= S) {
        minLength = Math.min(minLength, windowEnd - windowStart + 1);
        windowSum -= arr[windowStart]; // subtract the element going out
        windowStart++; // slide the window ahead
      }
    }
    return minLength == Integer.MAX_VALUE ? 0 : minLength;
  }

  public static void main(String[] args) {
    int result = MinSizeSubArraySum.findMinSubArray(7, new int[] { 2, 1, 5, 2, 3, 2 });
    System.out.println("Smallest subarray length: " + result);
  }
}