DouKaku? 5276 pooq: 十進BASIC Ver7.0.4の2進モ...(コラッツ・角谷の問題)

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十進BASIC Ver7.0.4の2進モードで。
実行環境は、pentiumM 1.3GHz、メモリ256MB、WindowsXPです。 

f( 837799 ) = 524 
 3.15000000000873 sec

!コラッツ・角谷の問題
LET  st = TIME
LET  n = 2^20
DIM  c(n)

FUNCTION f(k)
   IF k = 1 THEN
      LET  f = 0
   ELSEIF k <= n AND c(k) <> 0 THEN
      LET  f = c(k)
   ELSE
      IF  MOD(k,2) = 0  THEN
         LET  s = f(k / 2) + 1
      ELSE
         LET  s = f((3 *  k + 1) / 2) + 2
      END IF
      IF k <= n THEN  LET  c(k) = s 
      LET  f = s
   END IF
END FUNCTION 

LET  mx = f(n)
LET  no = n
FOR i = 3 TO n STEP 2
   LET  j = f(i)
   IF j > mx THEN 
      LET  mx = j
      LET  no = i
   END IF
NEXT I 
PRINT "f(";no;") =";mx
PRINT TIME - st;"sec"
END

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