sub fisher_yates_shuffle { my $array = shift; my $i; for ($i = @$array; --$i; ) { my $j = int rand ($i+1); next if $i == $j; @$array[$i,$j] = @$array[$j,$i]; } }
And permuting your version:
for (0..($#arr-1)) { $n = int (rand() * ($#arr - $_ + 1)) + $_; $t = $arr[$n]; $arr[$n] = $arr[$_]; $arr[$_] = $t; }
for (0..($#arr-1)) { $n = int (rand() * ($#arr - $_ + 1)) + $_;
$t = $arr[$n]; $arr[$n] = $arr[$_]; $arr[$_] = $t;
}
for (0..($#arr-1)) { $n = int (rand() * ($#arr - $_ + 1)) + $_;
@$arr[$_,$n] = @$arr[$n,$_];
}
for (0..($#arr-1)) { $n = int (rand() * ($#arr - $_ + 1)) + $_;
# next if $_ == $n;
@$arr[$_,$n] = @$arr[$n,$_]; }
The remaining two lines are functionally equivalent:
for (0..($#arr-1)) { # Your Version $n = int (rand() * ($#arr - $_ + 1)) + $_; for ($i = @$array; --$i; ) { # Fisher-Yates my $j = int rand ($i+1);
Frankly, I prefer your formulation (with the addition of the next if line) as it doesn't use an incomplete for loop, but the codes are equivalent.
UPDATE: For the benefit of the astute who realized that the remaining two lines weren't entirely equivalent:
for (0..($#arr-1)) { $n = int (
rand() * ($#arr - $_ + 1)
) + $_; # next if $_ == $n; @$arr[$_,$n] = @$arr[$n,$_]; }
for (0..($#arr-1)) { $n = int (
rand($#arr - $_ + 1)
) + $_; # next if $_ == $n; @$arr[$_,$n] = @$arr[$n,$_]; }
for (0..($#arr-1)) { $n = int (rand($#arr - $_ + 1))
+ $_
; # next if $_ == $n; @$arr[$_,$n] = @$arr[$n,$_]; }
Fisher-Yates traverses down the array, whereas this version traverses up the array (due to the appended + $_). Remove the addition and the codes are equivalent; leave it in and the codes are functionally equivalent.
In reply to Re^2: unsorted list
by eibwen
in thread unsorted list
by thekestrel
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