The target here would be half of the sum of all the elements in the input array. The idea is to recursively select each element and see if it can be used to reach the target.
1. If start_index >= length of the array, return true if the target is zero, false otherwise.
2. Include the first first number and check the remaining elements i.e. groupSum(start_index+1, arr,target - arr[start_index]))
3. Exclude the first number and check the same the remaining elements i.e. groupSum(start_index+1, arr, target)
