Submission #1189676

#	Time	Username	Problem	Language	Result	Execution time	Memory
1189676		Ardelion	Three Friends (BOI14_friends)	C++20	0 / 100	57 ms	10212 KiB

friends

#include <bits/stdc++.h>
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("O3")
//#pragma GCC target("avx2")

using namespace std;

//#define int          long long
#define ll           long long
#define X            first
#define Y            second
#define lc           (id<<1)
#define rc           (lc|1)
#define mid          ((l+r+1)>>1)
#define pb           push_back
#define lb           lower_bound
#define ub           upper_bound
#define mp           make_pair
#define sep          ' '
#define endl         "\n"
#define migmig       ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define FileIO       freopen("input.txt", "r", stdin); freopen("output.txt", "w", stdout);
#define all(x)       x.begin(), x.end()
#define ret(x)       {cout << x << endl; return;}

typedef pair<int, int> pii;
typedef pair<ll , ll > pll;

const int N     = 2e6+13;
const int LOG   = 23;
const int MOD   = 1e9 + 7; //998244353; //1e9+9;
const int BASE  = 691;
const int INF   = 1e9; //1e18;
const int dx[4] = {1, -1, 0,  0};
const int dy[4] = {0,  0, 1, -1};

ll md(ll x) {x%=MOD; return (x < 0 ? x+MOD : x);}
ll GCD(ll _a, ll _b) { return (!_b ? _a : GCD(_b, _a % _b)); }
ll POW(ll _a, ll _b) { return !_b ? 1 : ((_b & 1 ? _a : 1) * POW(_a * _a % MOD, _b / 2)) % MOD;}

int n, h1, h2, omit;
int p[N];
string s;
vector<int> ans;

void PREP() {
    p[0] = 1;
    for(int i = 1; i < N; i++) {
        p[i] = md(p[i-1] * BASE);
    }
}

void F() {
    cin >> n >> s;
    if(!(1&n)) ret("NOT POSSIBLE");
    omit = n>>1;
    for(int i = 0; i < (n>>1); i++) {
        h1 = md(h1 + s[i] * p[i]);
    }
    for(int i = omit+1; i < n; i++) {
        h2 = md(h2 + s[i] * p[i-omit-1]);
    }
    if(h1 == h2) ans.pb(omit);
    while(omit > 0) {
        h1 = md(h1 - s[omit-1] * p[omit-1]);
        h1 = md(h1 + s[omit] * p[omit-1]);
        omit --;
        if(h1 == h2) ans.pb(omit);
    }
    omit = n>>1; h1 = h2 = 0;
    for(int i = 0; i < (n>>1); i++) {
        h1 = md(h1 + s[i] * p[i]);
    }
    for(int i = omit+1; i < n; i++) {
        h2 = md(h2 + s[i] * p[i-omit-1]);
    }
    while(omit < n-1) {
        h2 = md(h2 - s[omit+1] * p[omit-(n>>1)]);
        h2 = md(h2 + s[omit] * p[omit-(n>>1)]);
        omit ++;
        if(h1 == h2) ans.pb(omit);
    }
    if(ans.empty()) ret("NOT POSSIBLE");
    if(ans.size() > 1) ret("NOT UNIQUE");
    string t = "";
    for(int i = 0; i < n; i++) {
        if(i != ans[0]) t.pb(s[i]);
    }
    while(t.size() > (n>>1)) t.pop_back();
    ret(t);
}

int32_t main() {
    migmig;
    PREP();
    int t=1;
    //cin >> t;
    while(t--)
        F();
    return 0;
}

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