River Crossing River Monks Medium — Set 100

Medium River Crossing Puzzle #100

Title

Medium River Crossing Puzzle #100

Scenario

Monks at the River

Narrative

An elder monk and two young monks must cross a river. The boat can carry only 1 adult or up to 2 young monks.

Entities

• {"id":"m1","name":"Elder Monk","icon":"\ud83e\uddd8"}
• {"id":"m2","name":"Young Monk A","icon":"\ud83e\uddd2"}
• {"id":"m3","name":"Young Monk B","icon":"\ud83e\uddd2"}

BoatCapacity

1

Constraints

• The boat can carry either 1 adult or 2 children.
• At least one person must row the boat.
• The elder monk cannot be left alone on a bank with both young monks unsupervised across the river.

Question

Describe a valid sequence of crossings that gets everyone to the other side without violating any constraint. What is the minimum number of trips required?

Solution

• {"trip":1,"direction":"\u2192","carrying":["Young A","Young B"],"leftBank":"Elder","rightBank":"Young A,Young B","note":"Both young monks cross."}
• {"trip":2,"direction":"\u2190","carrying":["Young A"],"leftBank":"Elder,Young A","rightBank":"Young B","note":"Young A returns."}
• {"trip":3,"direction":"\u2192","carrying":["Elder"],"leftBank":"Young A","rightBank":"Elder,Young B","note":"Elder crosses."}
• {"trip":4,"direction":"\u2190","carrying":["Young B"],"leftBank":"Young A,Young B","rightBank":"Elder","note":"Young B returns."}
• {"trip":5,"direction":"\u2192","carrying":["Young A","Young B"],"leftBank":"","rightBank":"All","note":"Both young monks cross. Done!"}

MinimumTrips

5

Hint

The first 2 move(s) of the solution are shown below to help you start.

PartialSolutionHint

• {"trip":1,"direction":"\u2192","carrying":["Young A","Young B"],"leftBank":"Elder","rightBank":"Young A,Young B","note":"Both young monks cross."}
• {"trip":2,"direction":"\u2190","carrying":["Young A"],"leftBank":"Elder,Young A","rightBank":"Young B","note":"Young A returns."}