Submission #226889

#	Time	Username	Problem	Language	Result	Execution time	Memory
226889		rqi	Three Friends (BOI14_friends)	C++14	100 / 100	208 ms	38808 KiB

friends

#include <bits/stdc++.h>
using namespace std;
 
typedef long long ll;
typedef long double ld;
typedef double db; 
typedef string str; 

typedef pair<int,int> pi;
typedef pair<ll,ll> pl; 
typedef pair<db,db> pd; 

typedef vector<int> vi; 
typedef vector<ll> vl; 
typedef vector<db> vd; 
typedef vector<str> vs; 
typedef vector<pi> vpi;
typedef vector<pl> vpl; 
typedef vector<pd> vpd; 

#define mp make_pair 
#define f first
#define s second
#define sz(x) (int)x.size()
#define all(x) begin(x), end(x)
#define rall(x) (x).rbegin(), (x).rend() 
#define rsz resize
#define ins insert 
#define ft front() 
#define bk back()
#define pf push_front 
#define pb push_back
#define eb emplace_back 
#define lb lower_bound 
#define ub upper_bound 

#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i,a) ROF(i,0,a)
#define trav(a,x) for (auto& a: x)

const int MOD = 1e9+7; // 998244353;
const int MX = 2e5+5; 
const ll INF = 1e18; 
const ld PI = acos((ld)-1);
const int xd[4] = {1,0,-1,0}, yd[4] = {0,1,0,-1}; 

template<class T> bool ckmin(T& a, const T& b) { 
    return b < a ? a = b, 1 : 0; }
template<class T> bool ckmax(T& a, const T& b) { 
    return a < b ? a = b, 1 : 0; } 
int pct(int x) { return __builtin_popcount(x); } 
int bit(int x) { return 31-__builtin_clz(x); } // floor(log2(x)) 
int cdiv(int a, int b) { return a/b+!(a<0||a%b == 0); } // division of a by b rounded up, assumes b > 0 

// INPUT
template<class A> void re(complex<A>& c);
template<class A, class B> void re(pair<A,B>& p);
template<class A> void re(vector<A>& v);
template<class A, size_t SZ> void re(array<A,SZ>& a);

template<class T> void re(T& x) { cin >> x; }
void re(db& d) { str t; re(t); d = stod(t); }
void re(ld& d) { str t; re(t); d = stold(t); }
template<class H, class... T> void re(H& h, T&... t) { re(h); re(t...); }

template<class A> void re(complex<A>& c) { A a,b; re(a,b); c = {a,b}; }
template<class A, class B> void re(pair<A,B>& p) { re(p.f,p.s); }
template<class A> void re(vector<A>& x) { trav(a,x) re(a); }
template<class A, size_t SZ> void re(array<A,SZ>& x) { trav(a,x) re(a); }

// TO_STRING
#define ts to_string
template<class A, class B> str ts(pair<A,B> p);
template<class A> str ts(complex<A> c) { return ts(mp(c.real(),c.imag())); }
str ts(bool b) { return b ? "true" : "false"; }
str ts(char c) { str s = ""; s += c; return s; }
str ts(str s) { return s; }
str ts(const char* s) { return (str)s; }
str ts(vector<bool> v) { 
    bool fst = 1; str res = "{";
    F0R(i,sz(v)) {
        if (!fst) res += ", ";
        fst = 0; res += ts(v[i]);
    }
    res += "}"; return res;
}
template<size_t SZ> str ts(bitset<SZ> b) {
    str res = ""; F0R(i,SZ) res += char('0'+b[i]);
    return res; }
template<class T> str ts(T v) {
    bool fst = 1; str res = "{";
    for (const auto& x: v) {
        if (!fst) res += ", ";
        fst = 0; res += ts(x);
    }
    res += "}"; return res;
}
template<class A, class B> str ts(pair<A,B> p) {
    return "("+ts(p.f)+", "+ts(p.s)+")"; }

// OUTPUT
template<class A> void pr(A x) { cout << ts(x); }
template<class H, class... T> void pr(const H& h, const T&... t) { 
    pr(h); pr(t...); }
void ps() { pr("\n"); } // print w/ spaces
template<class H, class... T> void ps(const H& h, const T&... t) { 
    pr(h); if (sizeof...(t)) pr(" "); ps(t...); }

// DEBUG
void DBG() { cerr << "]" << endl; }
template<class H, class... T> void DBG(H h, T... t) {
    cerr << to_string(h); if (sizeof...(t)) cerr << ", ";
    DBG(t...); }
#ifdef LOCAL // compile with -DLOCAL
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "]: [", DBG(__VA_ARGS__)
#else
#define dbg(...) 42
#endif

// FILE I/O
void setIn(string s) { freopen(s.c_str(),"r",stdin); }
void setOut(string s) { freopen(s.c_str(),"w",stdout); }
void unsyncIO() { ios_base::sync_with_stdio(0); cin.tie(0); }
void setIO(string s = "") {
    unsyncIO();
    // cin.exceptions(cin.failbit); 
    // throws exception when do smth illegal
    // ex. try to read letter into int
    if (sz(s)) { setIn(s+".in"), setOut(s+".out"); } // for USACO
}

mt19937 rng((uint32_t)chrono::steady_clock::now().time_since_epoch().count()); 

/**
 * Description: Polynomial hash for substrings with two bases.
 * Source:
    * KACTL
    * https://codeforces.com/contest/1207/submission/59309672
 * Verification: 
    * USACO Dec 17 Plat 1
    * CF Check Transcription
 */

typedef array<int,2> T; // bases not too close to ends 
uniform_int_distribution<int> BDIST(0.1*MOD,0.9*MOD);
const T base = {BDIST(rng),BDIST(rng)};
/// const T ibase = {(int)inv(mi(base[0])),(int)inv(mi(base[1]))};
T operator+(T l, T r) { 
    F0R(i,2) if ((l[i] += r[i]) >= MOD) l[i] -= MOD;
    return l; }
T operator-(T l, T r) { 
    F0R(i,2) if ((l[i] -= r[i]) < 0) l[i] += MOD;
    return l; }
T operator*(T l, T r) { 
    F0R(i,2) l[i] = (ll)l[i]*r[i]%MOD;
    return l; }
T makeT(char c) { return {c,c}; }
vector<T> pows = {{1,1}};
struct HashRange {
    str S; vector<T> cum = {{0,0}};
    void add(char c) { S += c; cum.pb(base*cum.bk+makeT(c)); }
    void add(str s) { trav(c,s) add(c); }
    void extend(int len) { while (sz(pows) <= len) pows.pb(base*pows.bk); }
    T hash(int l, int r) { int len = r+1-l; extend(len);
        return cum[r+1]-pows[len]*cum[l]; }
    /**int lcp(HashRange& b) { return first_true([&](int x) { 
        return cum[x] != b.cum[x]; },0,min(sz(S),sz(b.S)))-1; }*/
};
/// HashRange H; H.add("ababab"); F0R(i,6) FOR(j,i,6) ps(i,j,H.hash(i,j));

set<string> ans;
set<T> hashes;
HashRange H;


int main() {
    setIO();
    int N;
    string U;
    cin >> N >> U;
    if(N % 2 == 0){
        ps("NOT POSSIBLE");
        return 0;
    }
    H.add(U);

    for(int i = 0; i < N; i++){
        if(i <= N/2){
            if(H.hash(0, i-1) == H.hash(N/2+1, N/2+i) && H.hash(i+1, N/2) == H.hash(N/2+i+1, N-1)){
                T val = H.hash(N/2+1, N-1);
                if(hashes.find(val) == hashes.end()){
                    ans.ins(U.substr(N/2+1, N/2));
                    hashes.ins(val);
                }
                
            }
        }
        else{
            if(H.hash(0, i-1-N/2) == H.hash(N/2, i-1) && H.hash(i-N/2, N/2-1) == H.hash(i+1, N-1)){
                T val = H.hash(0, N/2-1);
                if(hashes.find(val) == hashes.end()){
                    ans.ins(U.substr(0, N/2));
                    hashes.ins(val);
                }
                
            }
        }
        if(sz(ans) > 1){
            ps("NOT UNIQUE");
            return 0;
        }
    }

    if(sz(ans) == 0){
        ps("NOT POSSIBLE");
        return 0;
    }
    if(sz(ans) > 1){
        ps("NOT UNIQUE");
        return 0;
    }
    ps(*ans.begin());
    return 0;
    // you should actually read the stuff at the bottom
}

/* stuff you should look for
    * int overflow, array bounds
    * special cases (n=1?)
    * do smth instead of nothing and stay organized
    * WRITE STUFF DOWN
*/

Compilation message (stderr)

friends.cpp: In function 'void setIn(std::__cxx11::string)':
friends.cpp:123:31: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
 void setIn(string s) { freopen(s.c_str(),"r",stdin); }
                        ~~~~~~~^~~~~~~~~~~~~~~~~~~~~
friends.cpp: In function 'void setOut(std::__cxx11::string)':
friends.cpp:124:32: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
 void setOut(string s) { freopen(s.c_str(),"w",stdout); }
                         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

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