characterNgrams function
Returns character n-grams of s with length n.
Overlapping windows; empty string or n < 1 returns empty list.
Implementation
List<String> characterNgrams(String s, int n) {
if (n < 1 || s.length < n) return <String>[];
final int count = s.length - n + 1;
return List.generate(count, (int i) {
final int end = (i + n).clamp(0, s.length);
return s.substringSafe(i, end);
});
}