Data update

Task/Hailstone-sequence/DuckDB/hailstone-sequence.duckdb

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+# Generate the hailstone sequence without an index
+create or replace function hailstone(start) as table (
+  with recursive cte as (
+    select start as n
+    union all
+    select if( n % 2 = 0, n // 2, 3 * n + 1) as n
+    from cte
+    where n != 1
+  ) from cte
+);
+
+# The length of the hailstone sequence of nn using count()
+create or replace function hailstone_length(nn) as (
+  select count() as n from hailstone(nn)
+);
+
+# Return a tuple giving the seed and the hailstone sequence length
+create or replace function hailstone_max_of_lengths(mx) as (
+  select max_by( (n,hailstone_length(n)), hailstone_length(n))
+  from range(1,mx+1) _(n)
+);
+
+# Table of lengths (e.g. for use with histogram())
+create or replace function hailstone_lengths(mx) as table (
+  select hailstone_length(n) as length
+  from range(1,mx+1) _(n)
+);