OraQA

The following is an interesting problem posted by mathforum.org:

Use all the digits from 1 to 9 without repeating, to form two numbers such that their product is maximum. A digit used should be unique across both the numbers. For example, the numbers formed could be 1234 and 56789.

—————————————— SQL Solution——————————————————

SELECT n1, n2, product as MAX_PRODUCT
FROM
(SELECT max(n1 * n2 ) over ( ) max_product, n1, n2, n1 * n2 product
 FROM
 (
  WITH DATA AS
  (SELECT replace(sys_connect_by_path(num, ','), ',') str_num
   FROM (SELECT LEVEL num FROM dual CONNECT BY LEVEL <10)
   WHERE LEVEL = 9
   START WITH num = 9
   CONNECT BY NOCYCLE PRIOR num != num
   AND LEVEL <= 9
  )
  SELECT to_number(substr(str_num,0,LEVEL)) n1, to_number(substr(str_num,LEVEL+1)) n2
  FROM DATA
  CONNECT BY PRIOR str_num = str_num
    AND LEVEL <= length(str_num)-1
  AND PRIOR DBMS_RANDOM.STRING ('P',20) IS NOT NULL
 )
)
WHERE max_product = product;

        N1                  N2                   MAX_PRODUCT
----------               ----------                -----------
      9642                87531                      843973902

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