Perl, 68 56 44

Like many other solutions, this uses the Fisher-Yates algorithm.

Using nutki's comment, 12 characters are saved by using $_ instead of $i and performing the operations in the array indices.

44:

sub f{@_[$_,$j]=@_[$j=rand$_,--$_]for 1..@_}

56:

sub f{$i=@_;$j=int(rand$i),@_[$i,$j]=@_[$j,$i]while$i--}

This is my first codegolf.

Perl, 68 56 44

Like many other solutions, this uses the Fisher-Yates algorithm.

Using nutki's comment, 12 characters are saved by using $_ instead of $i and performing the operations in the array indices.

44:

sub f{@_[$_,$j]=@_[$j=rand$_,--$_]for 1..@_}

56:

sub f{$i=@_;$j=int(rand$i),@_[$i,$j]=@_[$j,$i]while$i--}

This is my first codegolf.

Perl, 68 56

Like many other solutions, this uses the Fisher-Yates algorithm.

Updated to use array slicing.

sub f{$i=@_;$j=int(rand$i),@_[$i,$j]=@_[$j,$i]while$i--}

This is my first codegolf.

Perl, 68 56 44

Like many other solutions, this uses the Fisher-Yates algorithm.

Using nutki's comment, 12 characters are saved by using $_ instead of $i and performing the operations in the array indices.

44:

sub f{@_[$_,$j]=@_[$j=rand$_,--$_]for 1..@_}

56:

sub f{$i=@_;$j=int(rand$i),@_[$i,$j]=@_[$j,$i]while$i--}

This is my first codegolf.

Perl - 68 56

Like many other solutions, this uses the Fisher-Yates algorithm.

Updated to use array slicing.

sub f{$i=@_;$j=int(rand$i),@_[$i,$j]=@_[$j,$i]while$i--}

This is my first codegolf.

Perl, 68 56

Like many other solutions, this uses the Fisher-Yates algorithm.

Updated to use array slicing.

sub f{$i=@_;$j=int(rand$i),@_[$i,$j]=@_[$j,$i]while$i--}

This is my first codegolf.