wu :: forums - Print Page


    
      
        wu :: forums
        (http://www.ocf.berkeley.edu/~wwu/cgi-bin/yabb/YaBB.cgi)
      

        riddles >> medium >> River Crossing (III)
        
(Message started by: THUDandBLUNDER on Jun 1^st, 2003, 4:37am)

Title: River Crossing (III)
Post by THUDandBLUNDER on Jun 1^st, 2003, 4:37am

Three couples must cross a river to the other side. No wife can be in the presence of another man without her jealous husband being present. If the boat holds only two people, how many trips are necessary to get everyone across without anyone losing their honour?

Title: Re: River Crossing (III)
Post by redPEPPER on Jun 2^nd, 2003, 4:34am

This one is pretty linear again, as there's only one thing you can do if you don't want to go backwards. H1 to H3 are the husbands, W1 to W3 are the respective wives, b is the boat, ~~ is the river.

[hide]
H1 H2 H3 W1 W2 W3 b
~~~~~~~~~~
.

H1 H2 W1 W2
~~~~~~~~~~
H3 W3 b

H1 H2 H3 W1 W2 b
~~~~~~~~~~
W3

H1 H2 H3
~~~~~~~~~~
W1 W2 W3 b

H1 H2 H3 W3 b
~~~~~~~~~~
W1 W2

H3 W3
~~~~~~~~~~
H1 H2 W1 W2 b

H2 H3 W2 W3 b
~~~~~~~~~~
H1 W1

W2 W3
~~~~~~~~~~
H1 H2 H3 W1 b

W1 W2 W3 b
~~~~~~~~~~
H1 H2 H3

W1
~~~~~~~~~~
H1 H2 H3 W2 W3 b

W1 W2 b
~~~~~~~~~~
H1 H2 H3 W3

.
~~~~~~~~~~
H1 H2 H3 W1 W2 W3 b

[/hide]

Title: Re: River Crossing (III)
Post by FiBsTeR on Jul 17^th, 2007, 6:07pm

Prove that for any number of couples greater than three, it is NOT possible for the husbands and wives to cross a river on a raft that carries only two people, and with the condition that no wife can be left with another man without her husband present.

Title: Re: River Crossing (III)
Post by FiBsTeR on Jul 22^nd, 2007, 5:29am

Hint: [hide].kroW[/hide]