Rebalance Bank Accounts to a Minimum Balance

Stripe tracks money across bank accounts and sometimes moves funds so that every account stays at or above a required minimum balance.

Each input row is accountName,balance. Return a working sequence of transfers in the form from,to,amount that leaves every account with at least threshold.

An optimal number of transfers is not required. For deterministic output, process underfunded accounts in input order and take funds from overfunded accounts in input order. Move as much as possible in each transfer without taking a donor below the threshold or raising the current receiver above it.

Interview follow-up: Minimum transfer count

The graded rebalanceAccounts method above remains unchanged. As an additional ungraded practice exercise, implement minimumTransfersAboveTarget(accounts, target), returning an integer minimum number of transfers. Use the same accountName,balance row representation, but require each final balance to be strictly greater than the variable integer target.

For this follow-up, assume 1 to 12 uniquely named accounts, nonnegative integer balances and target at most 1,000,000, and enough total money: sum(balance) >= accounts.length * (target + 1). Any two distinct accounts may exchange a positive integer amount without making a balance negative. Only the count is returned; the order of an optimal sequence is irrelevant. The interface, integer units, feasibility, direct-transfer rules and finite bounds are authored practice assumptions.

Because balances are integers, strictly greater than target means at least target + 1. This conversion applies to the follow-up only. The graded method still uses its inclusive threshold argument, its input-order greedy serialization, and its existing 500-account limit.

For accounts = ["a,8","b,7","c,13","d,12"] and target = 9, return 2. Send 2 from d to a and 3 from c to b; every account then has at least 10. The graded constructor with threshold 10 uses three input-order transfers and is still correct for its own task.

For accounts = ["a,0","b,2"] and target = 0, return 1: both accounts must finish at least 1. Returning zero would silently replace the strict target with an inclusive boundary.