Can you solve the bridge riddle? - Alex Gendler
Audio Brief
Show transcript
This episode explores a classic bridge and torch logic puzzle, challenging listeners to optimize resource use under strict time constraints.
There are three key takeaways from this problem. The puzzle involves four survivors with varied crossing times, a 17-minute limit, and one lantern. A key insight is minimizing wasted time from the slowest individuals.
The optimal solution often involves a counterintuitive step: having the two slowest cross together, then using the fastest person for efficient return trips with the lantern. Solving such complex optimization problems requires accounting for every step, including return journeys, to accurately calculate total time and resources.
This riddle highlights the importance of strategic planning over intuitive approaches in resource-constrained scenarios.
Episode Overview
- An animated riddle presents a high-stakes logic puzzle involving a zombie apocalypse.
- Four survivors—an intern, a lab assistant, a janitor, and a professor—must cross a rickety bridge to escape an approaching horde.
- The puzzle is governed by strict constraints: a 17-minute time limit, a bridge that holds only two people, and a single lantern required for any crossing.
- Each person takes a different amount of time to cross (1, 2, 5, and 10 minutes), and the challenge is to find a sequence that gets everyone safely across in time.
Key Concepts
- This episode illustrates a classic "bridge and torch" or "river crossing" logic puzzle, which requires careful planning and optimization to solve.
- The core of the problem is managing a limited resource (the lantern) and minimizing the total time by strategically sequencing movements.
- The solution demonstrates that the most intuitive approach (sending the fastest people back and forth) is not always the most efficient.
- The key insight is to minimize the time wasted by the slowest individuals by having them cross the bridge together, even though it requires careful planning for the return trips with the lantern.
Quotes
- At 00:57 - "By the professor's calculations, the zombies will catch up to you in just over 17 minutes. So you only have that much time to get everyone across and cut the ropes." - This quote establishes the critical time constraint and the urgency of the situation.
- At 02:12 - "The key is to minimize the time wasted by the two slowest people by having them cross together." - This quote from the solution reveals the central strategy required to solve the riddle.
Takeaways
- To solve complex optimization problems, focus on minimizing the impact of the slowest or most resource-intensive steps.
- The fastest members of a group should be utilized for tasks that save the most time overall, such as making quick return trips.
- The optimal solution often involves a counterintuitive step; here, it's having the two slowest people cross together.
- In sequential planning, every step, including return trips, must be accounted for to accurately calculate the total time or resources used.
