PROG-1154: Longest Repeated Substring

#include <bits/stdc++.h>
using namespace std;
using lli = long long;
using pii = pair<int,int>;
const lli PB = 98765431;
string S;
int main(){

    int n,mx=0,cnt,m;
    scanf("%d%d",&n,&m);
    cin>>S;

    int l=0,r=n-1;
    while(l<=r){
        int mid=(l+r)/2;
        map <lli,int> cnt;
        lli hsh=0, rem=1;
        bool T=false;
        for(int i=0;i<mid;i++){
            if(i!=0) rem = rem*PB;
            hsh = hsh*PB+S[i];
        }
        for(int i=0;i<n;i++){
            if(i!=0) hsh = hsh*PB + S[i+mid-1];
            cnt[hsh]++;
            if(cnt[hsh]==m){
                T=true;
                break;
            }
            if(i+mid>=n) break;
            hsh = hsh-rem*S[i];
        }

        if(T) {
            mx=max(mx,mid);
            l = mid+1;
        }
        else  {
            r = mid-1;
        }
    }

    printf("%d",mx);

    return 0;
}