the-dao

Repair this code

Pay out a list of withdrawal requests without ever handing over money the account does not have.

today's brief

June 17, 2016. The DAO was a smart contract holding around 150 million dollars of other people's ether, and its withdrawal code checked the balance before sending the money but updated it afterwards. An attacker called back into it before the update landed, so the same balance kept authorising fresh payouts. About 3.6 million ether walked out, and Ethereum ended up splitting into two chains over how to answer it. Here is the same vault.

See it in action

drain(100, {60,60}, 2)

Expected result

Your checklist

For your own tracking. Tests grade your code.

balance is what the account holds. request lists n withdrawals, handled in order.
A request is paid only when the account still holds at least that amount, and refusing one does not stop the ones after it.
Return the total actually paid out.

More examples

drain(50, {10,50,40}, 3)

Expected result

drain(100, {101}, 1)

Expected result

Constraints

Expected files

vault.c

Allowed functions

None. Write every helper yourself.

Back to compete

Solutions

the-dao

Repair this code

Pay out a list of withdrawal requests without ever handing over money the account does not have.

today's brief

See it in action

drain(100, {60,60}, 2)

Expected result

Your checklist

For your own tracking. Tests grade your code.

balance is what the account holds. request lists n withdrawals, handled in order.
A request is paid only when the account still holds at least that amount, and refusing one does not stop the ones after it.
Return the total actually paid out.

More examples

drain(50, {10,50,40}, 3)

Expected result

drain(100, {101}, 1)

Expected result

Constraints

Expected files

vault.c

Allowed functions

None. Write every helper yourself.

Back to compete

Solutions