expert Set 42 Logic Puzzle

Tower of Hanoi: 3 Disks — Expert #42

Show solution

[{"step":1,"from":"A","to":"C","diskSize":1,"description":"Move disk 1 (smallest) from peg A to peg C."},{"step":2,"from":"A","to":"B","diskSize":2,"description":"Move disk 2 (second largest) from peg A to peg B."},{"step":3,"from":"C","to":"B","diskSize":1,"description":"Move disk 1 (smallest) from peg C to peg B."},{"step":4,"from":"A","to":"C","diskSize":3,"description":"Move disk 3 (largest) from peg A to peg C."},{"step":5,"from":"B","to":"A","diskSize":1,"description":"Move disk 1 (smallest) from peg B to peg A."},{"step":6,"from":"B","to":"C","diskSize":2,"description":"Move disk 2 (second largest) from peg B to peg C."},{"step":7,"from":"A","to":"C","diskSize":1,"description":"Move disk 1 (smallest) from peg A to peg C."}]

Title
Tower of Hanoi: 3 Disks — Expert #42
DiskCount
3
TaskType
error-identify
Pegs
A: Peg A (Start)
B: Peg B (Spare)
C: Peg C (Goal)
InitialState
A: [3,2,1]
B: []
C: []
TargetState
A: []
B: []
C: [3,2,1]
Solution
  • {"step":1,"from":"A","to":"C","diskSize":1,"description":"Move disk 1 (smallest) from peg A to peg C."}
  • {"step":2,"from":"A","to":"B","diskSize":2,"description":"Move disk 2 (second largest) from peg A to peg B."}
  • {"step":3,"from":"C","to":"B","diskSize":1,"description":"Move disk 1 (smallest) from peg C to peg B."}
  • {"step":4,"from":"A","to":"C","diskSize":3,"description":"Move disk 3 (largest) from peg A to peg C."}
  • {"step":5,"from":"B","to":"A","diskSize":1,"description":"Move disk 1 (smallest) from peg B to peg A."}
  • {"step":6,"from":"B","to":"C","diskSize":2,"description":"Move disk 2 (second largest) from peg B to peg C."}
  • {"step":7,"from":"A","to":"C","diskSize":1,"description":"Move disk 1 (smallest) from peg A to peg C."}
ErroneousSolution
  • {"step":1,"from":"A","to":"C","diskSize":1,"description":"Move disk 1 (smallest) from peg A to peg C."}
  • {"step":2,"from":"A","to":"B","diskSize":2,"description":"Move disk 2 (second largest) from peg A to peg B."}
  • {"step":3,"from":"C","to":"B","diskSize":1,"description":"Move disk 1 (smallest) from peg C to peg B."}
  • {"step":4,"from":"C","to":"A","diskSize":3,"description":"Move disk 3 from peg C to peg A."}
  • {"step":5,"from":"B","to":"A","diskSize":1,"description":"Move disk 1 (smallest) from peg B to peg A."}
  • {"step":6,"from":"B","to":"C","diskSize":2,"description":"Move disk 2 (second largest) from peg B to peg C."}
  • {"step":7,"from":"A","to":"C","diskSize":1,"description":"Move disk 1 (smallest) from peg A to peg C."}
ErrorStep
4
OptimalMoveCount
7
Question
The move sequence below contains exactly one illegal move. Identify the step number that violates the rules and explain why it is wrong.
Rules
  • Only one disk may be moved at a time.
  • A disk can only be placed on top of a larger disk or on an empty peg.
  • You must move the entire stack from peg A to peg C.
Hint
An illegal move places a larger disk on top of a smaller one, or moves a disk that is not on top of its stack.