Largest palindrome product: Difference between revisions
→{{header|FreeBASIC}}: added a fast secound version
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=={{header|FreeBASIC}}==
===Version 1===
<lang freebasic>function make_pal( n as ulongint ) as ulongint
'turn a number into a palindrom with twice as many digits
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nextd: 'yes, I used a goto. sue me.
next d</lang>
{{out}}
<pre>99 * 91 = 9009
993 * 913 = 906609
9999 * 9901 = 99000099
99979 * 99681 = 9966006699
999999 * 999001 = 999000000999
9998017 * 9997647 = 99956644665999</pre>
===Version 2===
This version is based on Version 1 with only a few changes and a option for using goto, exit or continue. It fast enough to go for n = 9 (highest possible for unsigned 64bit integers).
<lang freebasic>' version 06-10-2021
' compile with: fbc -s console
' Now you can choice, no speed changes for all 3
' 1: use goto
' 2: use exit
' 3: use continue
#Define Option_ 1 ' set option_ to 1, 2 or 3. for all other value's uses 1
Function make_pal( n As UInteger ) As ULongInt
'turn a number into a palindrom with twice as many digits
Dim As String ns = Str(n), ret = ns
For i As UInteger = Len(ns) To 1 Step -1
ret += Mid(ns, i, 1)
Next i
Return ValULng(ret)
End Function
Dim As ULongInt np
Dim As Double t1 =Timer
For d As UInteger = 2 To 9
For n As UInteger = 10^d -1 To 10^(d -1) Step -1 'count down from 999...
'since the first good number we encounter
'must be the highest
np = make_pal( n ) 'produce a 2d-digit palindrome from it
For f As uinteger = 10^d -1 To Sqr(np) Step -2 '10^(d-1) step -1 'look for highest d-digit factor
If np Mod f = 0 Then
Print f; " * "; np \ f; " = "; np
#If (option_ = 2)
Exit For, For
#ElseIf (option_ = 3)
Continue For, For, For
#Else
GoTo nextd
#EndIf
End If
Next f
Next n
#If (option_ <> 2 Or option_ <> 3)
nextd:
#EndIf
Next d
' empty keyboard buffer
While InKey <> "" : Wend
Print : Print "hit any key to end program"
Sleep
End</lang>
{{out}}
<pre>99 * 91 = 9009
993 * 913 = 906609
9999 * 9901 = 99000099
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999999 * 999001 = 999000000999
9998017 * 9997647 = 99956644665999
99999999 * 99990001 = 9999000000009999
999980347 * 999920317 = 999900665566009999</pre>
=={{header|Go}}==
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