KMP C++

#include <iostream>
#include <string>
#include <vector>

using namespace std;

string t,s;
int n,m;
vector<int> b;

void kmp_pre()
{
    b.resize(m+1);
    b[0] = -1;

    int i=0,j=-1;
    while(i<m)
    {
        while((j>=0) && (s[i]!=s[j])) j=b[j];
        i++;j++;
        b[i] = j;
    }
}

vector<int> kmp()
{
    vector<int> ans;
    int i=0,j=0;
    while(i<n)
    {
        while((j>=0) && (t[i]!=s[j])) j=b[j];
        i++; j++;
        if(j==m)
        {
            ans.push_back(i-j);
            j = b[j];
        }
    }
    return ans;
}

int main()
{
    t = "I DO NOT LIKE SEVENTY SEV BUT SEVENTY SEVENTY SEVEN";
    s = "SEVENTY SEVEN";
    n = t.size(), m = s.size();
    kmp_pre();
    vector<int> ans = kmp();

    cout << "Matches: ";
    for(int e:ans) cout << e << ' ';
    cout << '\n';
}