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  CMPU-145, Fall 2012
  Lab 2
  Solutions
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  1:  Range
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**** Version 1:  RANGE using MAP and REM-DUPES

(range '((1 2) (1 3) (1 4) (2 3) (2 4) (3 5) (3 1) (1 6))) ====> (2 3 4 5 1 6)
(range '((1 a) (1 b) (1 c) (2 a) (3 a) (4 b) (4 c) (5 c) (4 d) (5 a))) ====> (b c d a)
(range ()) ====> ()

**** Version 2:  RANGE-WR using accumulator-based helper function, RANGE-ACC

(range-wr '((1 2) (1 3) (1 4) (2 3) (2 4) (3 5) (3 1) (1 6))) ====> (6 1 5 4 3 2)
(range-wr '((1 a) (1 b) (1 c) (2 a) (3 a) (4 b) (4 c) (5 c) (4 d) (5 a))) ====> (d c b a)
(range-wr ()) ====> ()

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  2: Converse
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(converse '((1 2) (1 3) (1 4) (2 3) (2 4))) ====> ((2 1) (3 1) (4 1) (3 2) (4 2))
(converse ()) ====> ()
(converse '((1 a) (1 b) (1 c) (2 b) (2 e) (1 f) (1 g))) ====> ((a 1) (b 1) (c 1) (b 2) (e 2) (f 1) (g 1))

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  3:  Symmetric?
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**** Version 1:  Using REMOVE to get rid of pairs that are no longer needed

(symmetric? ()) ====> #t
(symmetric? '((1 2) (3 4) (5 6) (4 3) (6 5) (3 3) (2 1))) ====> #t
(symmetric? '((1 2) (3 4) (5 6) (4 3) (2 4))) ====> #f
**** Version 2:  Calling a helper function that keeps track of original list of pairs

(symmetrick? ()) ====> #t
(symmetrick? '((1 2) (3 4) (5 6) (4 3) (6 5) (3 3) (2 1))) ====> #t
(symmetrick? '((1 2) (3 4) (5 6) (4 3) (2 4))) ====> #f

**** Version 3:  Using MAP

(symm? ()) ====> #t
(symm? '((1 2) (3 4) (5 6) (4 3) (6 5) (3 3) (2 1))) ====> #t
(symm? '((1 2) (3 4) (5 6) (4 3) (2 4))) ====> #f
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