Submission #380408

#	Time	Username	Problem	Language	Result	Execution time	Memory
380408		SavicS	Three Friends (BOI14_friends)	C++14	0 / 100	107 ms	96400 KiB

friends

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <bits/stdc++.h>

#define fi first
#define se second
#define pb push_back
#define sz(a) (int)a.size()
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define ff(i,a,b) for(int i=a;i<=b;i++)
#define fb(i,b,a) for(int i=b;i>=a;i--)

using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef pair<int,int> pii;
const int maxn = 2000005;
const int inf = 1e9 + 5;

template<typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

// os.order_of_key(k) the number of elements in the os less than k
// *os.find_by_order(k)  print the k-th smallest number in os(0-based)

int n;
string s;

// Double Hashing - O(n)
const int mod1 = 1e9 + 7;
ll add1(ll a, ll b) {
	return (a + b) % mod1;
}
ll sub1(ll a, ll b) {
	return (a - b + mod1) % mod1;
}
ll mul1(ll a, ll b) {
	return (a * b) % mod1;
}
ll power1(ll a, ll b) {
	if(!b)return 1;
	ll pola = power1(a, b / 2);
	pola = mul1(pola, pola);
	if(b % 2)pola = mul1(pola, a);
	return pola;
}
ll inv1(ll a) {
	return power1(a, mod1 - 2);
}

// --------------------------------------------------------------

const int mod2 = 1e9 + 7;
ll add2(ll a, ll b) {
	return (a + b) % mod2;
}
ll sub2(ll a, ll b) {
	return (a - b + mod2) % mod2;
}
ll mul2(ll a, ll b) {
	return (a * b) % mod2;
}
ll power2(ll a, ll b) {
	if(!b)return 1;
	ll pola = power2(a, b / 2);
	pola = mul2(pola, pola);
	if(b % 2)pola = mul2(pola, a);
	return pola;
}
ll inv2(ll a) {
	return power2(a, mod1 - 2);
}

const int p1 = 31;
const int p2 = 33;
ll pw1[maxn];
ll pw2[maxn];
ll invz1[maxn];
ll invz2[maxn];
void init_hsh() {
	pw1[0] = 1;
	pw2[0] = 1;
	ff(i,1,maxn - 1) {
		pw1[i] = mul1(pw1[i - 1], p1);
		pw2[i] = mul2(pw2[i - 1], p2);
	}
	invz1[maxn - 1] = inv1(pw1[maxn - 1]);
	invz2[maxn - 1] = inv2(pw2[maxn - 1]);
	fb(i,maxn - 2, 0) {
		invz1[i] = mul1(invz1[i + 1], p1);
		invz2[i] = mul2(invz2[i + 1], p2);
	}
}

ll hsh1[maxn];
ll get1(int l, int r) {
	return mul1(sub1(hsh1[r], hsh1[l - 1]), invz1[l - 1]);
}

ll hsh2[maxn];
ll get2(int l, int r) {
	return mul2(sub2(hsh2[r], hsh2[l - 1]), invz2[l - 1]);
}

int main() {
	ios::sync_with_stdio(false);
	cout.tie(nullptr);
	cin.tie(nullptr);
	cin >> n >> s;
	if(n % 2 == 0)return cout << "NOT POSSIBLE", 0;
	init_hsh();
	ff(i,0,n - 1) {
		hsh1[i + 1] = add1(hsh1[i], mul1(pw1[i], s[i] - 'A' + 1));
		hsh2[i + 1] = add1(hsh2[i], mul1(pw2[i], s[i] - 'A' + 1));
	}
	int len = (n - 1) / 2;

	int rez = 0;
	int L = 0, R = -1;
	ff(i,1,len) {
		// brisem i-ti
		ll a11 = hsh1[i - 1];
		ll a12 = mul1(pw1[i - 1], get1(i + 1, len + 1));
		ll a1 = a11 + a12;

		ll a21 = hsh2[i - 1];
		ll a22 = mul2(pw2[i - 1], get2(i + 1, len + 1));
		ll a2 = a21 + a22;

		ll b1 = get1(len + 2, n);
		ll b2 = get2(len + 2, n);
		if(a1 == b1 && a2 == b2) {
			rez += 1;
			L = len + 2;
			R = n;
		}
	}

	ff(i,len + 1,n){
		// brisem i-ti
		ll a11 = get1(len + 1, i - 1);
		ll a12 = mul1(pw1[i - len - 1], get1(i + 1, n));
		ll a1 = a11 + a12;
		
		ll a21 = get2(len + 1, i - 1);
		ll a22 = mul2(pw2[i - len - 1], get2(i + 1, n));
		ll a2 = a21 + a22;
		
		ll b1 = hsh1[len];
		ll b2 = hsh2[len];
		
		if(a1 == b1 && a2 == b2){
			rez += 1;
			L = 1;
			R = len;
		}
	}

	if(rez > 1) {
		cout << "NOT UNIQUE" << endl;
		return 0;
	}
	ff(i,L - 1,R - 1)cout << s[i];
	cout << endl;

	return 0;
}
/**



// probati bojenje sahovski ili slicno

**/

• Subtask 1: 0 / 35
• Subtask 2: 0 / 65