Fastest Way To Find Mismatch Positions Between Two Strings of the Same Length

Question

I have a millions of pairs of string of same length which I want to compare and find the position where it has mismatches.

For example for each $str1 a

Answer 1

You're making 2 calls to substr for each character comparison which is probably what's slowing you down.

A few optimizations I would make

@source = split //,$str_source  #split first rather than substr
@base = split //, $str_base

for $i (0 .. length($str_source)) {
   $mism_pos{$1} = 1 if ($source[$i] ne $base); #hashing is faster than array push
}

return keys $mism_pos