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#! /usr/bin/env gforth
\ Challenge 102
\
\ TASK #1 � Rare Numbers
\ Submitted by: Mohammad S Anwar
\
\ You are given a positive integer $N.
\
\ Write a script to generate all Rare numbers of size $N if exists. Please
\ checkout the page for more information about it.
\ Examples
\
\ (a) 2 digits: 65
\ (b) 6 digits: 621770
\ (c) 9 digits: 281089082
\ 1234 -> 4321
: invert_number { n -- }
0 { n1 }
BEGIN n 0<> WHILE
n1 10 * n 10 MOD + TO n1
n 10 / TO n
REPEAT
n1 ;
\ check if number is perfect square
: is_perfect_square ( n -- f )
S>F FSQRT
FDUP FLOOR F= IF TRUE ELSE FALSE THEN ;
\ compute 10^n
: 10pow ( n -- 10^n )
1 SWAP
0 ?DO
10 *
LOOP ;
: .rare { n -- }
n 10pow n 1- 10pow DO
I I invert_number { r r1 }
r r1 + is_perfect_square IF
r r1 >= IF
r r1 - is_perfect_square IF
r . CR
THEN THEN THEN
LOOP ;
NEXT-ARG S>NUMBER? 0= THROW DROP
.rare
BYE
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