Sunday, August 23

skype-storm

daily challenge16

today's brief

August 16, 2007. A Patch Tuesday reboot cycle brings millions of Windows machines back up in the same minute, and every Skype client on them tries to log in at once. The login network buckles. Clients that got refused retried straight away, at full speed, so the queue never drained. Two days of darkness for 220 million accounts. Make the client wait longer each time it is turned away.

Objective

Return the wait the client should sit through after a run of login attempts.

Steps

ok lists n login attempts in the order they were made. ok[i] is 1 when attempt i was accepted and 0 when it was refused.
The wait starts at 1 second. Every refusal doubles it, and it never goes above 32.
An accepted attempt puts the wait back to 1.
Return the wait once all n attempts have been handled.

examples

$ backoff({0,0,0}, 3)

$ backoff({0,0,1,0}, 4)

$ backoff({1}, 1)

Constraints

Expected files

backoff.c

Allowed functions

None. Write every helper yourself.

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Solutions

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