Revise paste Untitled

#include <iostream>
#include <set>
#include <vector>
#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 10;
typedef long long ll;
const ll MOD = 922337186621;
const ll alphabet_size = 52;
int n, k;
int rolling_hash(string & s) {
    set<ll> st;
    int n = (int) s.size();
    vector<ll> powers(n + 1, 1);
    for(int i = 1; i <= n; i++) {
        powers[i] = (powers[i - 1] * alphabet_size) % MOD;
    }
    ll hash = 0;
    for(int i = 0; i < k; i++) {
        hash = (hash * alphabet_size + s[i]) % MOD;
    }
    st.insert(hash);
    for(int i = 1; i <= n - k; i++) {
        hash = (hash - powers[k - 1] * s[i - 1]);
        while(hash < 0) {
            hash += MOD;
        }
        hash %= MOD;
        hash = (hash * alphabet_size + s[i + k - 1]) % MOD;
        st.insert(hash);
    }
    return (int) st.size();
    
}

int main()
{
    ios_base::sync_with_stdio(false);
    int t;
    cin >> t;
    while(t--) {
        cin >> n >> k;
        string s;
        cin >> s;
        cout << rolling_hash(s) << endl;
    }
    return 0;
}