'''

static int maxSubsetSumRecursion(vector& arr, int l, int r) { // TODO check null assert( arr );

// tolerating l > r as an indication of an empty set,
// but r - l shouldn't be less than -1
int size = (r-l)+1;
assert( size >= -1 );
if( size < 0 ) {
    size = 0;
}

// Return base cases up to size == 2
if( 0 == size ) return 0;
if( 1 == size ) return max( arr[l], 0 );
if( 2 == size ) return max( max(arr[l], arr[r]), 0 );

// given a midpoint cell (index k = floor(n/2)):
// Case 1: int at cell [k] is in solution
//     (Note: all ints in solution must be positive integers)
// Case 2: int at cell [k] is not in solution
const unsigned int k = l + (size/2);  // floor division

int sum1 = 0;
if( arr[k] > 0 ){
    sum1 = arr[k] + 
           maxSubsetSumRecursion( arr, l, k-2 ) +
           maxSubsetSumRecursion( arr, k+2, r );
}
int sum2 = maxSubsetSumRecursion( arr, l, k-1 ) +
           maxSubsetSumRecursion( arr, k+1, r );

return max(sum1, sum2);

}

'''