Submission #31381

#	Time	Username	Problem	Language	Result	Execution time	Memory
31381		imaxblue	Three Friends (BOI14_friends)	C++14	100 / 100	146 ms	23484 KiB

friends

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define mp make_pair
#define pb push_back
#define x first
#define y second
#define pii pair<int, int>
#define p3i pair<pii, int>
#define pll pair<ll, ll>
#define p3l pair<pll, ll>
#define lseg L, (L+R)/2, N*2+1
#define rseg (L+R)/2+1, R, N*2+2
#define ub upper_bound
#define lb lower_bound
#define pq priority_queue
#define MN 1000000007
#define fox(k, x) for (int k=0; k<x; ++k)
#define fox1(k, x) for (int k=1; k<=x; ++k)
#define foxr(k, x) for (int k=x-1; k>=0; --k)
#define fox1r(k, x) for (int k=x; k>0; --k)
#define ms multiset
#define flood(x) memset(x, 0x3f3f3f3f, sizeof x)
#define drain(x) memset(x, 0, sizeof x)
#define rng() (rand() >> 3)*rand()

int n, c[2], p=-1, ans, seed=1337, k[2000005], hsh[2000005], hsh2;
string s;
int main(){
    //cin.sync_with_stdio(0);
    //cin.tie(0);
    //cout.sync_with_stdio(0);
    //cout.tie(0);
    cin >> n >> s;
    n=s.size();
    if (n%2==0){
        cout << "NOT POSSIBLE";
        return 0;
    }
    fox(l, n/2+1){
        c[s[l]==s[l+n/2]]++;
    }
    k[n-1]=1;
    foxr(l, n){
        hsh[l]=(hsh[l+1]+1LL*s[l]*k[l])%MN;
        if (l>0) k[l-1]=(1LL*k[l]*seed)%MN;
        //cout << hsh[l] << ' ';
    }
    //cout << endl;
    fox(l, n){
        if (l<=n/2)
            c[s[l]==s[l+n/2]]--;
        else
            c[s[l]==s[l-n/2-1]]--;
        if (c[0]==0){
            //    cout << (1LL*hsh2+hsh[l+1])%MN << endl;
            if (p!=-1 && (1LL*hsh2+hsh[l+1])%MN!=ans){
                cout << "NOT UNIQUE";
                return 0;
            }
            p=l;
            ans=(1LL*hsh2+hsh[l+1])%MN;
        }
        hsh2=(hsh2+1LL*k[l+1]*s[l])%MN;
        //cout << c[0] << endl;
        if (l<n/2)
            c[s[l]==s[l+n/2+1]]++;
        else
            c[s[l]==s[l-n/2]]++;
    }
    if (p==-1) cout << "NOT POSSIBLE";
    else {
        //if (p>=n) while(1);
        s.erase(p, 1);
        s.erase(0, n/2);
        cout << s;
    }
    return 0;
}

• Subtask 1: 35 / 35
• Subtask 2: 65 / 65