Submission #1189662

#	Time	Username	Problem	Language	Result	Execution time	Memory
1189662		Ardelion	Three Friends (BOI14_friends)	C++20	0 / 100	6 ms	5604 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     = 2e5+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, invBASE;
int p[N], ip[N], seg[N<<2], laz[N<<2];
string s;
vector<int> ans;

void update(int id, int x) {
    seg[id] = md(seg[id] * x);
    laz[id] = md(laz[id] * x);
}

void push(int id) {
    update(lc, laz[id]);
    update(rc, laz[id]);
    laz[id] = 1;
}

void build(int id, int l, int r) {
    laz[id] = 1;
    if(r-l == 1) {
        seg[id] = md(p[l] * s[l]);
        return;
    }
    build(lc, l, mid);
    build(rc, mid, r);
    seg[id] = md(seg[lc] + seg[rc]);
}

void upd(int id, int l, int r, int pos, int val) {
    if(r-l == 1) {
        seg[id] = md(val);
        return;
    }
    push(id);
    if(pos < mid) upd(lc, l, mid, pos, val);
    else upd(rc, mid, r, pos, val);
    seg[id] = md(seg[lc] + seg[rc]);
}

void mul(int id, int l, int r, int ql, int qr, int val) {
    if(r <= ql || qr <= l) return;
    if(ql <= l && r <= qr) {
        update(id, val);
        return;
    }
    push(id);
    mul(lc, l, mid, ql, qr, val);
    mul(rc, mid, r, ql, qr, val);
    seg[id] = md(seg[lc] + seg[rc]);
}

int get(int id, int l, int r, int ql, int qr) {
    if(r <= ql || qr <= l) return 0;
    if(ql <= l && r <= qr) return seg[id];
    push(id);
    return md(get(lc, l, mid, ql, qr) + get(rc, mid, r, ql, qr));
}

bool check(int i) {
    int x = get(1, 0, n, i, i+1);
    upd(1, 0, n, i, 0);
    mul(1, 0, n, i, n, ip[1]);
    int fh, sh, m;
    if(i < (n>>1)) {
        m = (n>>1)+1;
    }
    else {
        m = n>>1;
    }
    sh = get(1, 0, n, 0, m);
    fh = get(1, 0, n, m, n);
    fh = md(fh * ip[n>>1]);
    bool f = (fh == sh);
    // cout << m << sep << sh << sep << fh << sep;
    mul(1, 0, n, i, n, p[1]);
    upd(1, 0, n, i, x);
    return f;
}

void PREP() {
    p[0] = 1;
    for(int i = 1; i < N; i++) p[i] = md(p[i-1] * BASE);
    ip[N-1] = POW(p[N-1], MOD-2);
    for(int i = N-1; i > 0; i--) {
        ip[i-1] = md(ip[i] * BASE);
    }
}

void F() {
    cin >> n >> s;
    if(!(1&n)) ret("NOT POSSIBLE");
    build(1, 0, n);
    for(int i = 0; i < n; i++) {
        if(check(i)) ans.pb(i);
    }
    if(ans.size() == 0) {
        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);
    // cout << check(0);
    // cout << get(1, 0, n, 0, 3) << sep << md(get(1, 0, n, 4, 7) * ip[4]);
    // cout << md(ip[1] * BASE);
}

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

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