Submission #318182

#	Time	Username	Problem	Language	Result	Execution time	Memory
318182		Benq	Palinilap (COI16_palinilap)	C++14	100 / 100	198 ms	37308 KiB

palinilap

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

using pi = pair<int,int>;
using pl = pair<ll,ll>;
using pd = pair<db,db>;

using vi = vector<int>;
using vb = vector<bool>;
using vl = vector<ll>;
using vd = vector<db>; 
using vs = vector<str>;
using vpi = vector<pi>;
using vpl = vector<pl>; 
using vpd = vector<pd>;

#define tcT template<class T
#define tcTU tcT, class U
// ^ lol this makes everything look weird but I'll try it
tcT> using V = vector<T>; 
tcT, size_t SZ> using AR = array<T,SZ>; 
tcT> using PR = pair<T,T>;

// pairs
#define mp make_pair
#define f first
#define s second

// vectors
#define sz(x) (int)(x).size()
#define all(x) begin(x), end(x)
#define rall(x) (x).rbegin(), (x).rend() 
#define sor(x) sort(all(x)) 
#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 

// loops
#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; // not too close to LLONG_MAX
const ld PI = acos((ld)-1);
const int dx[4] = {1,0,-1,0}, dy[4] = {0,1,0,-1}; // for every grid problem!!
mt19937 rng((uint32_t)chrono::steady_clock::now().time_since_epoch().count()); 
template<class T> using pqg = priority_queue<T,vector<T>,greater<T>>;

// helper funcs
constexpr int pct(int x) { return __builtin_popcount(x); } // # of bits set
constexpr int bits(int x) { return 31-__builtin_clz(x); } // floor(log2(x)) 
ll cdiv(ll a, ll b) { return a/b+((a^b)>0&&a%b); } // divide a by b rounded up
ll fdiv(ll a, ll b) { return a/b-((a^b)<0&&a%b); } // divide a by b rounded down

tcT> bool ckmin(T& a, const T& b) {
	return b < a ? a = b, 1 : 0; } // set a = min(a,b)
tcT> bool ckmax(T& a, const T& b) {
	return a < b ? a = b, 1 : 0; }

tcTU> T fstTrue(T lo, T hi, U f) {
	hi ++; assert(lo <= hi); // assuming f is increasing
	while (lo < hi) { // find first index such that f is true 
		T mid = lo+(hi-lo)/2;
		f(mid) ? hi = mid : lo = mid+1; 
	} 
	return lo;
}
tcTU> T lstTrue(T lo, T hi, U f) {
	lo --; assert(lo <= hi); // assuming f is decreasing
	while (lo < hi) { // find first index such that f is true 
		T mid = lo+(hi-lo+1)/2;
		f(mid) ? lo = mid : hi = mid-1;
	} 
	return lo;
}
tcT> void remDup(vector<T>& v) { // sort and remove duplicates
	sort(all(v)); v.erase(unique(all(v)),end(v)); }
tcTU> void erase(T& t, const U& u) { // don't erase
	auto it = t.find(u); assert(it != end(t));
	t.erase(u); } // element that doesn't exist from (multi)set

// INPUT
#define tcTUU tcT, class ...U
tcT> void re(complex<T>& c);
tcTU> void re(pair<T,U>& p);
tcT> void re(vector<T>& v);
tcT, size_t SZ> void re(AR<T,SZ>& a);

tcT> 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); }
tcTUU> void re(T& t, U&... u) { re(t); re(u...); }

tcT> void re(complex<T>& c) { T a,b; re(a,b); c = {a,b}; }
tcTU> void re(pair<T,U>& p) { re(p.f,p.s); }
tcT> void re(vector<T>& x) { trav(a,x) re(a); }
tcT, size_t SZ> void re(AR<T,SZ>& x) { trav(a,x) re(a); }
tcT> void rv(int& n, vector<T>& x) { re(n); x.rsz(n); trav(a,x) re(a); }

// TO_STRING
#define ts to_string
str ts(char c) { return str(1,c); }
str ts(const char* s) { return (str)s; }
str ts(str s) { return s; }
str ts(bool b) { 
	#ifdef LOCAL
		return b ? "true" : "false"; 
	#else 
		return ts((int)b);
	#endif
}
tcT> str ts(complex<T> c) { 
	stringstream ss; ss << c; return ss.str(); }
str ts(vector<bool> v) {
	str res = "{"; F0R(i,sz(v)) res += char('0'+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; }
tcTU> str ts(pair<T,U> p);
tcT> str ts(T v) { // containers with begin(), end()
	#ifdef LOCAL
		bool fst = 1; str res = "{";
		for (const auto& x: v) {
			if (!fst) res += ", ";
			fst = 0; res += ts(x);
		}
		res += "}"; return res;
	#else
		bool fst = 1; str res = "";
		for (const auto& x: v) {
			if (!fst) res += " ";
			fst = 0; res += ts(x);
		}
		return res;

	#endif
}
tcTU> str ts(pair<T,U> p) {
	#ifdef LOCAL
		return "("+ts(p.f)+", "+ts(p.s)+")"; 
	#else
		return ts(p.f)+" "+ts(p.s);
	#endif
}

// OUTPUT
tcT> void pr(T x) { cout << ts(x); }
tcTUU> void pr(const T& t, const U&... u) { 
	pr(t); pr(u...); }
void ps() { pr("\n"); } // print w/ spaces
tcTUU> void ps(const T& t, const U&... u) { 
	pr(t); if (sizeof...(u)) pr(" "); ps(u...); }

// DEBUG
void DBG() { cerr << "]" << endl; }
tcTUU> void DBG(const T& t, const U&... u) {
	cerr << ts(t); if (sizeof...(u)) cerr << ", ";
	DBG(u...); }
#ifdef LOCAL // compile with -DLOCAL, chk -> fake assert
	#define dbg(...) cerr << "Line(" << __LINE__ << ") -> [" << #__VA_ARGS__ << "]: [", DBG(__VA_ARGS__)
	#define chk(...) if (!(__VA_ARGS__)) cerr << "Line(" << __LINE__ << ") -> function(" \
		 << __FUNCTION__  << ") -> CHK FAILED: (" << #__VA_ARGS__ << ")" << "\n", exit(0);
#else
	#define dbg(...) 0
	#define chk(...) 0
#endif

// FILE I/O
void setIn(str s) { freopen(s.c_str(),"r",stdin); }
void setOut(str s) { freopen(s.c_str(),"w",stdout); }
void unsyncIO() { cin.tie(0)->sync_with_stdio(0); }
void setIO(str 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
}

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

typedef array<int,2> H; // bases not too close to ends 
uniform_int_distribution<int> BDIST(0.1*MOD,0.9*MOD);
const H base = {BDIST(rng),BDIST(rng)};
/// const T ibase = {(int)inv(mi(base[0])),(int)inv(mi(base[1]))};
H operator+(H l, H r) { 
	F0R(i,2) if ((l[i] += r[i]) >= MOD) l[i] -= MOD;
	return l; }
H operator-(H l, H r) { 
	F0R(i,2) if ((l[i] -= r[i]) < 0) l[i] += MOD;
	return l; }
H operator*(H l, H r) { 
	F0R(i,2) l[i] = (ll)l[i]*r[i]%MOD;
	return l; }
H makeH(char c) { return {c,c}; }
/// H& operator+=(H& l, H r) { return l = l+r; }
/// H& operator-=(H& l, H r) { return l = l-r; }
/// H& operator*=(H& l, H r) { return l = l*r; }

vector<H> pows = {{1,1}};
struct HashRange {
	str S; vector<H> cum = {{0,0}};
	void add(char c) { S += c; cum.pb(base*cum.bk+makeH(c)); }
	void add(str s) { trav(c,s) add(c); }
	void extend(int len) { while (sz(pows) <= len) pows.pb(base*pows.bk); }
	H 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 HR; HR.add("ababab"); F0R(i,6) FOR(j,i,6) ps(i,j,HR.hash(i,j));

HashRange hr, hr_rev;
int N;

str W;
map<char,ll> ad[MX];
ll lin[MX], cons[MX];
ll ans;

H hash_nor(int l, int r) { return hr.hash(l,r); }
H hash_rev(int l, int r) { return hr_rev.hash(N-1-r,N-1-l); }

void sub_range(int l, int r) {
	if (l > r) return;
	auto add_linear = [&](int l, int r, int x) { lin[l] += x, lin[r] -= x; };
	auto add_cons = [&](int l, int r, int x) { cons[l] += x, cons[r] -= x; };
	add_linear(l,(l+r+1)/2,1);
	add_cons  (l,(l+r+1)/2,-(l-1));
	add_linear((l+r+2)/2,r+1,-1);
	add_cons  ((l+r+2)/2,r+1,r+1);
	// FOR(i,l,(l+r+1)/2) sub[i] += i-(l-1);
	// FOR(i,(l+r+2)/2,r+1) sub[i] += r+1-i;
	// int cnt = 0;
	// while (l < r) {
	// 	cnt ++;
	// 	sub[l] += cnt, sub[r] += cnt;
	// 	l ++, r --;
	// }
}

void account(int l, int r) {
	int mx = min(l,N-1-r);
	int len = lstTrue(0,mx,[&](int x){
		return hash_nor(l-x,r+x) == hash_rev(l-x,r+x);
	});
	ans += len + (l == r);
	sub_range(l-len,r+len); // l-len to r+len is a palindrome
	if (l-len > 0 && r+len < N-1) {
		int new_len = lstTrue(len+2,mx,[&](int x){
			return hash_nor(l-x,l-len-2) == hash_rev(r+len+2,r+x);
		});
		ad[l-len-1][W[r+len+1]] += new_len-len;
		ad[r+len+1][W[l-len-1]] += new_len-len;
	}
}

int main() {
	setIO(); re(W); N = sz(W);
	hr.add(W); reverse(all(W));
	hr_rev.add(W); reverse(all(W));
	F0R(i,N) account(i,i);
	F0R(i,N-1) account(i+1,i);
	FOR(i,1,N) lin[i] += lin[i-1], cons[i] += cons[i-1];
	ll bes = 0;
	F0R(i,N) trav(t,ad[i]) ckmax(bes,t.s-lin[i]*i-cons[i]);
	ps(bes+ans);
}

/* stuff you should look for
	* int overflow, array bounds
	* special cases (n=1?)
	* do smth instead of nothing and stay organized
	* WRITE STUFF DOWN
	* DON'T GET STUCK ON ONE APPROACH
*/

Compilation message (stderr)

palinilap.cpp: In function 'void setIn(str)':
palinilap.cpp:185:28: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
  185 | void setIn(str s) { freopen(s.c_str(),"r",stdin); }
      |                     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~
palinilap.cpp: In function 'void setOut(str)':
palinilap.cpp:186:29: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
  186 | void setOut(str s) { freopen(s.c_str(),"w",stdout); }
      |                      ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 17 / 17
• Subtask 2: 37 / 37
• Subtask 3: 46 / 46