Happy numbers: Difference between revisions

<syntaxhighlight lang="algolw">

begin % find some happy numbers: numbers whose digit-square sums become 1 %

% when repeatedly applied %

% returns true if n is happy, false otherwise %

logical procedure isHappy ( integer value n ) ;

% the largest digit-square sun for a 9 digit number is 729: 81 * 9 %

logical array seen ( 0 :: 729 );

integer v, dSum;

for i := 0 until 729 do seen( i ) := false;

v := abs n;

while begin

dSum := 0;

while v not = 0 do begin

integer d;

d := v rem 10;

v := v div 10;

dSum := dSum + ( d * d )

end while_v_ne_0 ;

dSum not = 1 and not seen( dSum )

end

do begin

seen( dSum ) := true;

v := dSum

end while_not_happy_and_not_looping ;

dSum = 1

end isHappy ;

begin % find the first 8 happy numbers %

integer n, hCount;

hCount := 0;

n := 1;

while hCount < 8 do begin

writeon( i_w := 1, s_w := 0, " ", n );

hCount := hCount + 1

end if_isHappy__n ;

end while_hCount_lt_10

end.

</syntaxhighlight>

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