A-M baby

Task/Executable-library/Factor/executable-library-2.factor

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+! rosetta/hailstone/length/length.factor
+USING: assocs kernel io math math.ranges prettyprint
+       rosetta.hailstone sequences ;
+IN: rosetta.hailstone.length
+
+<PRIVATE
+: f>0 ( object/f -- object/0 )
+    dup [ drop 0 ] unless ;
+
+: max-value ( pair1 pair2 -- pair )
+    [ [ second ] bi@ > ] most ;
+
+: main ( -- )
+    H{ } clone      ! Maps sequence length => count.
+    1 100000 [a,b) [
+        hailstone length                ! Find sequence length.
+        over [ f>0 1 + ] change-at      ! Add 1 to count.
+    ] each
+    ! Find the length-count pair with the highest count.
+    >alist unclip-slice [ max-value ] reduce
+    first2 swap
+    "Among Hailstone sequences from 1 <= n < 100000," print
+    "there are " write pprint
+    " sequences of length " write pprint "." print ;
+PRIVATE>
+
+MAIN: main