twitter-2020

Your mission

Find the first character in an address that is too easy to misread to be legal.

today's brief

July 15, 2020. A teenager talks his way into Twitter's internal admin panel, and 130 accounts start posting the same offer: send bitcoin, get double back. Obama, Musk, Apple, Uber. Twitter froze every verified account on the platform to stop it, by which point about 12 bitcoin had moved. Check an address before anyone sends anything.

See it in action

first_ambiguous("bc1qxy2kgd")

Expected result

-1

Your checklist

For your own tracking. Tests grade your code.

addr is a null terminated address.
Four characters are never used because they read alike: the digit zero, capital O, capital I and lowercase l.
Return the index of the first one of those four that appears in addr.
Return -1 when none of them appears.

More examples

first_ambiguous("l337")

Expected result

first_ambiguous("abcO0")

Expected result

Constraints

Expected files

addr.c

Allowed functions

None. Write every helper yourself.

Back to compete

Solutions

twitter-2020

Your mission

Find the first character in an address that is too easy to misread to be legal.

today's brief

See it in action

first_ambiguous("bc1qxy2kgd")

Expected result

-1

Your checklist

For your own tracking. Tests grade your code.

addr is a null terminated address.
Four characters are never used because they read alike: the digit zero, capital O, capital I and lowercase l.
Return the index of the first one of those four that appears in addr.
Return -1 when none of them appears.

More examples

first_ambiguous("l337")

Expected result

first_ambiguous("abcO0")

Expected result

Constraints

Expected files

addr.c

Allowed functions

None. Write every helper yourself.

Back to compete

Solutions