I did not benchmark this yet - but this should be faster (it passes your tests): 
sub twosum_NetWallah{
  my ($inp, $target)=@_;
  my %targ_idx = map { $inp->[$_] => $_ } 0..$#$inp;

  for (0..$#$inp){
     next unless defined ( my $other=$targ_idx{ $target - $inp->[$_] }
+ );
     next if $other == $_;
     return [ $other > $_ ? ($_, $other) : ($other, $_) ];
  }
  return undef;
}    

# Test NetWallah..
for my $test (@tests) {
    is_deeply
        sort_arrayref(twosum_NetWallah ($test->[INPUT], $test->[TARGET
+])),
        sort_arrayref($test->[EXPECTED]);
}

[download]
UPDATE 1: removed buggy " -1" from (0..$#$inp -1); deleted unnecessary variable @solutions.

UPDATE 2: I did try to benchmark the code - kcott's runs ~ 40% faster, so I was surprised!
However- After adding this test case: 

    [[-5,-3,1,4,7], 1, [1,3]],

[download]
kcott's code fails that test case, but mine passes.
Note - that new test case does meet the problem definition (array of integers), which can have negative numbers.
Also - kcott's code assumes and takes advantage of the input being sorted - input order is NOT specified in the problem definition.

BTW - thanks for setting up this challenge!

                "If you had better tools, you could more effectively demonstrate your total incompetence."

In reply to Re: LeetCode Problem #1 - Two Sum - Improve and/or discuss. by NetWallah
in thread LeetCode Problem #1 - Two Sum - Improve and/or discuss. by kcott

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