Anthropologists, Cannibals

by

Three anthropologists and three cannibals are making their way through a jungle and come to a river. They find a canoe large enough to carry only two persons at once. Only one of the anthropologists and one of the cannibals knows how to paddle this type of vessel. How many crossings will be needed to get all the travelers across, without ever letting the anthropologists be outnumbered by cannibals on either shore?


Show/Hide Solution

Here’s one way: (A & C are the paddlers)

A →  
a    
a    
C →  
c    
c    
  ← A
a    
a    
    C
c    
c    
A →  
a    
a    
    C
c →  
c    
    A
a    
a    
  ← C
    c
c    
    A
a    
a →  
C →  
    c
c    
    A
a    
    a
  ← C
    c
c    
    A
a →  
    a
C →  
    c
c    
    A
    a
    a
  ← C
    c
c    
    A
    a
    a
C →  
    c
c →  
     A
    a
    a
    C
    c
    c


This solution may be suspect, in that at stages 4 and 7 there are more c’s than a’s on one side, but only briefly, one hopes. Or is there a better solution?

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