Driver Balances with Cached Total Balance

You need to maintain balances for delivery drivers (driverId is a string or integer) and answer very frequent queries for the total balance across all drivers. Design a data structure / API supporting: add(driverId, delta): increase the driver’s balance by delta (delta can be negative). If the driver doesn’t exist, treat initial balance as 0. get(driverId): return the driver’s current balance; return 0 if missing. getTotal(): return the sum of balances of all drivers. Constraints/requirements: getTotal() is called extremely frequently (possibly inside loops), so it should be as fast as possible. State target time complexities and implement the core logic. Scale (for complexity reasoning): Number of operations Q up to 2e5 Number of distinct drivers N up to 2e5 delta in [-1e9, 1e9] Example: add(A,10), add(B,5), getTotal() => 15 add(A,-3), get(A) => 7, getTotal() => 12 get(C) => 0, getTotal() still 12 Example Input 9 add A 10 add B 5 getTotal add A -3 get A getTotal get C add C 8 getTotal Output 15 7 12 0 20