prefix_func.dg

int[] prefix_func(string s) {
	int[] p = int[s.len]
	int k = 0
	int i
	p[0] = 0
	for i = 1; i < s.len; i++ {
		[prob = 30; 'a' <= s[i] && s[i] <= 'z' && 'a' <= s[k] && s[k] <= 'z']
		while k > 0 && s[i] != s[k] {
			k = p[k-1]
		}
		if s[i] == s[k] {
			k++
		}
		p[i] = k
	}

	return p
}