River Crossing River Explorers Hard — Set 30

Hard River Crossing Puzzle #30

Title

Hard River Crossing Puzzle #30

Scenario

The Explorers

Narrative

Three explorers must cross a crocodile-infested river with their backpacks. The raft holds at most 2 items total (people + packs). Each explorer must keep their own backpack with them at all times.

Entities

• {"id":"e1","name":"Explorer 1","icon":"\ud83e\udded"}
• {"id":"e2","name":"Explorer 2","icon":"\ud83e\udded"}
• {"id":"e3","name":"Explorer 3","icon":"\ud83e\udded"}
• {"id":"b1","name":"Backpack A","icon":"\ud83c\udf92"}
• {"id":"b2","name":"Backpack B","icon":"\ud83c\udf92"}
• {"id":"b3","name":"Backpack C","icon":"\ud83c\udf92"}

BoatCapacity

2

Constraints

• The raft holds at most 2 items (person + pack count as separate items).
• An explorer's backpack must always travel with its owner.
• At least one explorer must operate the raft each crossing.

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":["E1+Pack A"],"leftBank":"E2,E3,B,C","rightBank":"E1,A","note":"Explorer 1 crosses with pack."}
• {"trip":2,"direction":"\u2190","carrying":["E1"],"leftBank":"E1,E2,E3,B,C","rightBank":"A","note":"E1 returns (pack stays)."}
• {"trip":3,"direction":"\u2192","carrying":["E2+Pack B"],"leftBank":"E1,E3,C","rightBank":"E2,A,B","note":"Explorer 2 crosses with pack."}
• {"trip":4,"direction":"\u2190","carrying":["E2"],"leftBank":"E1,E2,E3,C","rightBank":"A,B","note":"E2 returns."}
• {"trip":5,"direction":"\u2192","carrying":["E3+Pack C"],"leftBank":"E1,E2","rightBank":"E3,A,B,C","note":"Explorer 3 crosses with pack."}
• {"trip":6,"direction":"\u2190","carrying":["E3"],"leftBank":"E1,E2,E3","rightBank":"A,B,C","note":"E3 returns."}
• {"trip":7,"direction":"\u2192","carrying":["E1","E2"],"leftBank":"E3","rightBank":"E1,E2,A,B,C","note":"E1 and E2 cross."}
• {"trip":8,"direction":"\u2190","carrying":["E1"],"leftBank":"E1,E3","rightBank":"E2,A,B,C","note":"E1 returns for E3."}
• {"trip":9,"direction":"\u2192","carrying":["E1","E3"],"leftBank":"","rightBank":"All","note":"All across. Done!"}

MinimumTrips

9

Hint

The first 1 move(s) of the solution are shown below to help you start.

PartialSolutionHint

• {"trip":1,"direction":"\u2192","carrying":["E1+Pack A"],"leftBank":"E2,E3,B,C","rightBank":"E1,A","note":"Explorer 1 crosses with pack."}