Submission #889795

#	Time	Username	Problem	Language	Result	Execution time	Memory
889795		dwuy	Three Friends (BOI14_friends)	C++14	100 / 100	115 ms	68020 KiB

friends

/// dwuy: _,\,,,_\,__,\,,_
#include <bits/stdc++.h>

#define fastIO ios_base::sync_with_stdio(false); cin.tie(NULL)
#define file(a) freopen(a".inp","r",stdin); freopen(a".out", "w",stdout)
#define fi first
#define se second
#define endl "\n"
#define len(s) int32_t(s.length())
#define MASK(k)(1LL<<(k))
#define TASK ""
#define int long long

using namespace std;

typedef tuple<int, int, int> tpiii;
typedef pair<double, double> pdd;
typedef pair<int, int> pii;
typedef long long ll;

const long long OO = 1e18;
const int MOD1 = 998244353;
const int MOD2 = 1e9 + 7;
const int INF = 1e9;
const int MX = 2000005;
const int base = 307;

int n;
int pf1[MX];
int pf2[MX];
int bp1[MX];
int bp2[MX];
string s;

void nhap(){
    cin >> n;
    cin >> s;
    if(!(n&1)){
        cout << "NOT POSSIBLE";
        exit(0);
    }
}

int add1(int a, int b){
    a += b;
    return a + (a>=MOD1? -MOD1 : a<0? MOD1 : 0);
}

int mul1(int a, int b){
    return a*b%MOD1;
}

int add2(int a, int b){
    a += b;
    return a + (a>=MOD2? -MOD2 : a<0? MOD2 : 0);
}

int mul2(int a, int b){
    return a*b%MOD2;
}

int get1(int l, int r){
    return add1(pf1[r], -mul1(pf1[l-1], bp1[r-l+1]));
}

int get2(int l, int r){
    return add2(pf2[r], -mul2(pf2[l-1], bp2[r-l+1]));
}

void solve(){
    s = ' ' + s;
    bp1[0] = bp2[0] = 1;
    for(int i=1; i<=n; i++){
        bp1[i] = mul1(bp1[i-1], base);
        bp2[i] = mul2(bp2[i-1], base);
    }
    for(int i=1; i<=n; i++){
        pf1[i] = add1(mul1(pf1[i-1], base), s[i]);
        pf2[i] = add2(mul2(pf2[i-1], base), s[i]);
    }
    int flag = -1;
    int mid = (n+1)>>1;
    bool isUnique = 1;
    pii p = {-1, -1};
    pii pre = {get1(1, mid-1), get2(1, mid-1)};
    pii suf = {get1(mid+1, n), get2(mid+1, n)};
    for(int i=1; i<=mid; i++){
        int cur1 = add1(mul1(get1(1, i-1), bp1[mid-i]), get1(i+1, mid));
        int cur2 = add2(mul2(get2(1, i-1), bp2[mid-i]), get2(i+1, mid));
        pii cur = {cur1, cur2};
        if(cur == suf){
            flag = 0;
            if(p.fi < 0) p = cur;
            if(p != cur) isUnique = 0;
        }
    }
    for(int i=mid+1; i<=n; i++){
        int cur1 = add1(mul1(get1(mid, i-1), bp1[n-i]), get1(i+1, n));
        int cur2 = add2(mul2(get2(mid, i-1), bp2[n-i]), get2(i+1, n));
        pii cur = {cur1, cur2};
        if(cur == pre){
            flag = 1;
            if(p.fi < 0) p = cur;
            if(p != cur) isUnique = 0;
        }
    }
    if(flag == -1) cout << "NOT POSSIBLE", exit(0);
    if(!isUnique) cout << "NOT UNIQUE", exit(0);
    if(!flag) for(int i=mid+1; i<=n; i++) cout << s[i];
    else for(int i=1; i<mid; i++) cout << s[i];
}
int32_t main(){
    fastIO;
    //file(TASK);

    nhap();
    solve();

    return 0;
}

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