How can both teams signal task completion with cards? Go!

This week’s developer challenge is all about communication. How would you signal “we’re done” when two teams can only communicate with playing cards? 🃏 Drop your solutions in the comments!

Speaker: M.E Francis

[GoogleDevelopers]

Answer: The key is to use redundancy and majority voting within the constraints of the 52-card deck. Each team selects a specific rank (e.g., all Kings for Team A, all Queens for Team B) and places up to 4 cards of that rank in consecutive turns to signal “done.”
Even if cards are lost due to the wind, the majority of remaining cards can still reliably indicate the signal. To confirm acknowledgment, the other team responds with their own rank in the same redundant pattern.

This mirrors concepts like quorum-based consensus in distributed systems, where redundancy ensures reliability despite communication loss or failures.

[GoogleDevelopers]

Hint for this week’s puzzle: Timing is everything. Think about how cards could act as signals—and what kind of patterns would be easy to recognize.

[kmaughn]

Assuming they are in a room with a door each team should be listening for the opening and closing of a door. If a door is open the other door must remain close. Initially the first team to complete their challenge should open the door placing the card in the hallway then close the door. Correspondingly the second team on hearing closure should open their door immediately observing the card and working, on completion they should match the card observed with one from their deck, place it in the doorway and close their door to signal the end. The initial team will always be the team determining the card while the corresponding team presents matches for validation. The teams can go back and forth until they have exhausted all cards or Until either team stops presenting a card. The initial team would know their completion signal was seen by observing the matched card and the corresponding team would know theirs were observed by seeing the new issued card.

[NaveenReddy-pj]

Use a full house or four of a kind to signal 'we’re done'. Clear and easy to recognize!

[CypherSifr]

Signal task DONE only with cards, assuming that teams are aware of the challenge and rules: Place an ace of spades card in corridor = done. No card = not done.

[joeljose]

Either put the one card, or put none in respective scenario...only constraint is that only one card can be used so😅

[Propagandalf_der_raue]

How about we do team building exercises or speech courses? Or maybe they could just yell or even better... Put a door in the wall to connect the two offices 😅

[floydlobo]

Handshakes....with a timer, ⏳ on each side, something like this

[Truthunversity]

Sounds like they should shout done to me

[yemiodugbesan]

Sounds like sockets and webRtc Connections to me 😅

[HereTheHeckOfIt]

Stop throwing the cards. I'm not a programmer but it seems like something would need to terminate