trusting-trust

Your mission

Say whether every character of a mark appears in a binary in the same order.

today's brief

1984, Turing Award lecture. Ken Thompson explains how he put a backdoor in the Unix login program with nothing showing in the source. Teach the compiler to insert it, then teach the compiler to plant that lesson in its own next version. He closes by saying you cannot trust code you did not write yourself. Check whether the mark survived into the binary.

See it in action

survives("login", "l0o1g2i3n4")

Expected result

Your checklist

For your own tracking. Tests grade your code.

mark and code are both null-terminated strings.
Return 1 when the characters of mark all appear in code in that order, with anything at all allowed between them.
Return 0 otherwise.
An empty mark is always there.

More examples

survives("login", "nigol")

Expected result

survives("aab", "axaxb")

Expected result

Constraints

Expected files

trust.c

Allowed functions

None. Write every helper yourself.

Back to compete

Solutions

trusting-trust

Your mission

Say whether every character of a mark appears in a binary in the same order.

today's brief

See it in action

survives("login", "l0o1g2i3n4")

Expected result

Your checklist

For your own tracking. Tests grade your code.

mark and code are both null-terminated strings.
Return 1 when the characters of mark all appear in code in that order, with anything at all allowed between them.
Return 0 otherwise.
An empty mark is always there.

More examples

survives("login", "nigol")

Expected result

survives("aab", "axaxb")

Expected result

Constraints

Expected files

trust.c

Allowed functions

None. Write every helper yourself.

Back to compete

Solutions