1. Find if there is a subarray with 0 sum: http://www.geeksforgeeks.org/find-if-there-is-a-subarray-with-0-sum/
2. FInd subarray with given sum: http://www.geeksforgeeks.org/find-subarray-with-given-sum/
3. http://www.careercup.com/question?id=10796894