36 lines
602 B
Plaintext
36 lines
602 B
Plaintext
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###
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### fib11
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###
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## Chapter 5 section 4.3.1
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sub fib {
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my $n = shift;
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my ($s1, $return);
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my $BRANCH = 0;
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my @STACK;
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while (1) {
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if ($n < 2) {
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$return = $n;
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} else {
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if ($BRANCH == 0) {
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push (@STACK, [ $BRANCH, 0, $n ]), $n -= 1 while $n >= 2;
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$return = $n;
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} elsif ($BRANCH == 1) {
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push @STACK, [ $BRANCH, $return, $n ];
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$n -= 2;
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$BRANCH = 0;
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next;
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} elsif ($BRANCH == 2) {
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$return += $s1;
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}
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}
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return $return unless @STACK;
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($BRANCH, $s1, $n) = @{pop @STACK};
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$BRANCH++;
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}
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}
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