for $_ (  0..$#items  ) {
    # ...
    for $_ (  @{ $sum[@_] < $target
        ? [ ($_+1)..$#items ] : [] }
    ) {
        # ...
        for $_ (  @{ $sum[@_] < $target
            ? [ ($_+1)..$#items ] : [] }
        ) {
            # ...
        }
    }
}