With slight changes, this can be made tail-recursive, which means the recursion can be elimited completely.
Tail-recursive variant:
sub cleverGuess {
my( $lower, $higher ) = @_;
my $guess = int(($lower + $higher)/2);
print "Guessing: $guess\n";
if ($guess == $ans) {
print "The guess was correct!";
return;
}
elsif ($ans < $guess) {
print "Lower...";
$higher = $guess-1;
}
else {
print "Higher...";
$lower = $guess + 1;
}
cleverGuess($lower, $higher);
}
Tail-recursion replaced with a loop:
sub cleverGuess {
my( $lower, $higher ) = @_;
for (;;) {
my $guess = int(($lower + $higher)/2);
print "Guessing: $guess\n";
if ($guess == $ans) {
print "The guess was correct!";
return;
}
elsif ($ans < $guess) {
print "Lower...";
$higher = $guess-1;
}
else {
print "Higher...";
$lower = $guess + 1;
}
}
}
I don't mean to diminish your effort. I just wish to illustrate that power of recursion is sometimes an illusion. Performance should increase by removing recursion where it's not needed, and now you know how!
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