Or maybe like this:

# look for @AoA row and col containing index
# for first non-zero element in @A
for my $index (0..$#A) {
   if ($A[$index]) {
      ROW:
      for my $row (0..$#AoA) {
         for my $col (0..$#{$AoA[$row]}) {
            if ($AoA[$row][$col] == $index) {
               print "$row $col\n";
               last ROW;
            }
         }
      }

      last;
   }
}
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