polar-lander

Your mission

Return the cycle where the leg switch has genuinely found the ground.

today's brief

December 3, 1999. Mars Polar Lander goes quiet on the way down and is never heard from again. The best reconstruction runs like this. The legs snap open at 1500 metres and the switches inside them twitch. Flight software writes the twitch down as a landing, and when it starts polling at 40 metres the flag is already sitting there. Engines off. Forty metres left to fall. Take the reading twice before you believe it.

See it in action

touchdown({1,0,1,0,1,1,0}, 7, 0)

Expected result

Your checklist

For your own tracking. Tests grade your code.

sensor holds n readings of the leg switch, one per cycle, each 0 or 1.
Anything before index armed comes from the legs deploying and does not count.
The ground is confirmed at index i when the readings at i and at i + 1 are both 1, with i at or after armed.
Return the first index that confirms it, and -1 when nothing does.

More examples

touchdown({1,1,0,0,1,1}, 6, 2)

Expected result

touchdown({1,0,1,0}, 4, 0)

Expected result

-1

Constraints

Expected files

legs.c

Allowed functions

None. Write every helper yourself.

Back to compete

Solutions

polar-lander

Your mission

Return the cycle where the leg switch has genuinely found the ground.

today's brief

See it in action

touchdown({1,0,1,0,1,1,0}, 7, 0)

Expected result

Your checklist

For your own tracking. Tests grade your code.

sensor holds n readings of the leg switch, one per cycle, each 0 or 1.
Anything before index armed comes from the legs deploying and does not count.
The ground is confirmed at index i when the readings at i and at i + 1 are both 1, with i at or after armed.
Return the first index that confirms it, and -1 when nothing does.

More examples

touchdown({1,1,0,0,1,1}, 6, 2)

Expected result

touchdown({1,0,1,0}, 4, 0)

Expected result

-1

Constraints

Expected files

legs.c

Allowed functions

None. Write every helper yourself.

Back to compete

Solutions