Two-Sum - Range Allowance Algorithm Design
Create a Set searchSet to store the item's that have already been examined.

Iterate through the input Array of item capacities.
2a. Find the targetCapacity for the current item: totalCapacity - itemCapacity.
2b. Generate a targetCapacitiesArray plus and minus the totalCapacity and the range allowance provided.
2c. For each capacity in targetCapacitiesArray, see if each number is contained in the searchSet, and return true if found.
2d. Else, add the itemCapacity to the searchSet.

Return false if the entire input is iterated through without finding a match.