Minimum times A has to be repeated such that B is a substring of it

Given two strings A and B. Find minimum number of times A has to be repeated such that B is a Substring of it. If B can never be a substring then return -1.

• Time : O(m)
• Space : O(m)

class Solution {
    vector<int> PI(string& s) {
        int n = s.length();
        vector<int> pi(n);
        for(int i = 1, j = 0; i < n; i++) {
            while(j > 0 and s[i] != s[j]) j = pi[j - 1];
            if(s[i] == s[j]) pi[i] = ++j;
        }

        return pi;
    }
    int kmp(string s, string& t) {
        int n = s.length(), m = t.length();
        vector<int> pi = PI(t);
        for(int i = 0, j = 0; i < n; i++) {
            while(j > 0 and s[i] != t[j]) j = pi[j - 1];
            if(s[i] == t[j]) {
                if(++j == m)
                    return i;
            }
        }

        return -1;
    }
public:
    int minRepeats(string A, string B) {
        string s = "";
        int res = 0;
        while(s.length() < B.length()) {
            s += A;
            res++;
        }
        
        return kmp(s, B) != -1 ? res : kmp(s + A, B) != -1 ? res + 1 : -1;
    }
};