GPU Credits Grants: create_grant / subtract / get_balance with expiry and FIFO-by-expire deduction

Problem: GPU Credit Grants Implement a GPU credits ledger that supports creating grants, subtracting credits, and querying balance. Credits are issued as grants, each with an expiration time. When subtracting credits, you must deduct from grants in order of earliest expiration first. Implement the following operations (or equivalent methods): create_grant(grant_id, amount, expire_time): create a grant with amount credits that expires after expire_time (expired credits must not be used for future subtraction and must not be counted in balance queries). subtract(amount, time): perform a persistent deduction of amount credits at timestamp time. The deduction must consume remaining credits from non-expired grants, ordered by increasing expire_time. get_balance(time): return the available balance at timestamp time, excluding any remaining credits in grants that are expired at time. Deduction rules Only non-expired grants can be used. Deduct in increasing expire_time order. subtract mutates remaining credits and affects future subtract and get_balance calls. Constraints Up to 2 * 10^5 operations amount is a non-negative integer expire_time and time are integer timestamps Example test cases Deduct earliest-expiring first create_grant(A, 10, 5) create_grant(B, 10, 7) subtract(12, 4) get_balance(4) => 8 Expired credits not counted create_grant(A, 10, 5) get_balance(6) => 0 Subtraction affects the future create_grant(A, 10, 100) subtract(3, 1) get_balance(2) => 7 Skip expired grants when subtracting create_grant(A, 10, 5) create_grant(B, 10, 100) subtract(6, 10) get_balance(10) => 4 Insufficient balance behavior (needs clarification) create_grant(A, 5, 100) subtract(10, 1) get_balance(1) => ? (confirm expected behavior: clamp to 0 / error / return failure) Example Input create_grant A 10 5 create_grant B 10 7 subtract 12 4 get_balance 4 Output 8