1) the open || die statement should actually be

```open IN, \$infile or die "Can't open input file: \$!";
For reasons of precedence.

2) Here are some faster algorithms. One way is to use a hash to record which characters you've already placed into your substitution string. Here's the main loop:

```my %set;
my \$substit = "";
for (1..26) {
my \$randchar;
do { \$randchar = chr((int rand 26) + 65) }
while \$set{\$randchar}++;
\$substit .= \$randchar;
}
This way you don't have to do a search through the string each time.

And here's an even better way of doing it: build a random permutation of the alphabet string. To do this, we'll actually need an array:

```my @alpha = split //, "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
Now we set another array equal to this one, then call the random shuffle algorithm on it:
```my @crypt = @alpha;
fisher_yates_shuffle(\@crypt);
which shuffles the array in place. Now all you need to do is get back the substitution string:
```my \$substit = join '', @crypt;
Here's the definition of the fisher_yates_shuffle sub:
```sub fisher_yates_shuffle {
my \$array = shift;
for (my \$i = @\$array; --\$i; ) {
my \$j = int rand (\$i+1);
next if \$i == \$j;
@\$array[\$i, \$j] = @\$array[\$j, \$i];
}
return join '', @\$array;
}
(Taken directly from perlfaq4.)

I did some benchmarking on these, and here's what I got:

```Benchmark: timing 5000 iterations of orig, f_yates, hash...
orig: 33 secs (23.60 usr  0.00 sys = 23.60 cpu)
f_yates:  5 secs ( 2.88 usr  0.00 sys =  2.88 cpu)
hash: 13 secs ( 5.68 usr  0.00 sys =  5.68 cpu)
where "orig" is the one you posted, "f_yates" is the one using fisher_yates_shuffle, and "hash" is the one using a hash to record seen characters.

If I've messed anything up, let me know.

In reply to RE: Cryptogram Generator by btrott
in thread Cryptogram Generator by Elihu

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