Two Matches Gone Missing

To find s inside t, KMP concatenates them with a separator that appears in neither string, computes the prefix function of the whole thing, and reports a match wherever the value equals |s|. A reviewer removes the separator to save memory:

vector<int> pi = prefix_function(s + t);        // separator dropped
for (int i = s.size(); i < pi.size(); i++)
    if (pi[i] == (int)s.size())
        cout << i - 2 * s.size() + 1 << "\n";  // occurrence in t

Run it with s = "aa" and t = "aaa". The pattern really does occur in t, at positions 0 and 1. What does the loop print?

Nothing at all, because every prefix function value past the join is larger than |s|.

-1, and nothing else. Both real occurrences go unreported.

0 and 1, the correct answer. Removing the separator shortens the concatenation by one character, and the + 1 in the index formula already compensates for that.

0, 1 and one extra index outside t, so discarding out-of-range values repairs the code.