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Diffstat (limited to 'miralib/ex/barry.m')
| -rw-r--r-- | miralib/ex/barry.m | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/miralib/ex/barry.m b/miralib/ex/barry.m new file mode 100644 index 0000000..f93af80 --- /dev/null +++ b/miralib/ex/barry.m @@ -0,0 +1,31 @@ +||from Barry Brown, Sierra College -- Aug 2009 +||the critical case is test5, below + +|| Given a number, return the next number in the Collatz sequence +collatz :: num -> num +collatz n = n div 2, if (n mod 2 = 0) + = 3*n+1, if (n mod 2 = 1) + +|| Given a number, return the whole Collatz sequence starting with that +|| number. Note that it does not include the '1' on the end, but that's OK +|| since we're only interested in the length. +collatzseq n = takewhile (>1) (iterate collatz n) + +|| Given a number, return a tuple with the starting number and the +|| length of the Collatz sequence. We'll find the maximum tuple using the +|| next function. The number returned will be 1 less than the actual +|| Collatz sequence length, but that's OK for our purposes. One one of them +|| will be the longest. +collatzpair n = (n, #(collatzseq n)) + +|| Given two tuples, return the greater based on the second term. +maxtuple :: (*,**)->(*,**)->(*,**) +maxtuple x y = x, if (snd x > snd y) + = y, otherwise + + +test1 = map collatzpair [1..9] +test2 = foldr maxtuple (1,0) (map collatzpair [1..9]) +test3 = foldr maxtuple (1,0) (map collatzpair [1..999]) +test4 = foldr maxtuple (1,0) (map collatzpair [1..9999]) +test5 = foldl maxtuple (1,0) (map collatzpair [1..999999]) ||segfaults, ok with foldl |