getPi_function.cpp

vector<int> getPi(string p){
    int m = (int)p.size(), j=0;
    vector<int> pi(m, 0);
    for(int i = 1; i< m ; i++){
        while(j > 0 && p[i] !=  p[j])
            j = pi[j-1];
        if(p[i] == p[j])
            pi[i] = ++j;
    }
    return pi;
}