Submission #388116

#	Time	Username	Problem	Language	Result	Execution time	Memory
388116		Keshi	Palindromes (APIO14_palindrome)	C++17	73 / 100	1033 ms	59176 KiB

palindrome

//In the name of God
#include <bits/stdc++.h>
#pragma GCC optimize("O2")
using namespace std;

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

const ll maxn = 3e5 + 100;
const ll lg = 19;
const ll mod = 1e9 + 7;
const ll inf = 1e9;

#define fast_io ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define file_io freopen("input.txt", "r+", stdin);freopen("output.txt", "w+", stdout);
#define pb push_back
#define Mp make_pair
#define F first
#define S second
#define Sz(x) ll((x).size())
#define all(x) (x).begin(), (x).end()
#define lc (id << 1)
#define rc (lc | 1)

ll n, p[maxn], rnk[maxn], lcp[maxn], f[maxn];
string s;
vector<ll> vec[maxn];

ll mn[lg][maxn];

void bld(){
	for(ll i = 0; i < n + 1; i++){
		mn[0][i] = lcp[i];
	}
	for(ll i = 1; i < lg; i++){
		for(ll j = 0; j + (1 << i) <= n + 1; j++){
			mn[i][j] = min(mn[i - 1][j], mn[i - 1][j + (1 << (i - 1))]);
		}
	}
}
ll get(ll l, ll r){
	if(l == r) return inf;
	ll t = r - l;
	ll i = f[t];
	return min(mn[i][l], mn[i][r - (1 << i)]);
}

int main(){
	fast_io;
	for(ll i = 2; i < maxn; i++){
		f[i] = f[i / 2] + 1;
	}

	cin >> s;
	n = Sz(s);
	s += '#';
	vector<int> sa, rev;
	sa.resize(n+1);
      iota(sa.begin(),sa.end(),0);
      sort(sa.begin(),sa.end(),
           [&](int a,int b){
             if(s[a]==s[b]) return a>b;
             return s[a]<s[b];
           });
      vector<int> c(n+1,0),r(n+1),cnt(n+1);
      for(int i=0;i<=n;i++) r[i]=s[i];
      for(int len=1;len<=n;len*=2){
        for(int i=0;i<=n;i++){
          c[sa[i]]=i;
          if(i>0 &&
             r[sa[i-1]]==r[sa[i]] &&
             sa[i-1]+len<=n &&
             r[sa[i-1]+len/2]==r[sa[i]+len/2]) c[sa[i]]=c[sa[i-1]];
        }
        iota(cnt.begin(),cnt.end(),0);
        copy(sa.begin(),sa.end(),r.begin());
        for(int i=0;i<=n;i++){
          int s1=r[i]-len;
          if(s1>=0) sa[cnt[c[s1]]++]=s1;
        }
        c.swap(r);
      }
      rev.resize(n+1);
      for(int i=0;i<=n;i++) rev[sa[i]]=i;
	for(ll i = 0; i < n + 1; i++){
		p[i] = sa[i];
		rnk[i] = rev[i];
	}
	for(ll i = 0, k = 0; i < n + 1; i++){
		if(rnk[i] == n){
			k = 0;
			continue;
		}
		ll j = p[rnk[i] + 1];
		while(i + k < n + 1 && j + k < n + 1 && s[i + k] == s[j + k]) k++;
		lcp[rnk[i]] = k;
		if(k) k--;
	}
	bld();
	vector<int> d1(n);
	for (int i = 0, l = 0, r = -1; i < n; i++) {
   	 	int k = (i > r) ? 1 : min(d1[l + r - i], r - i + 1);
   	 	while (0 <= i - k && i + k < n && s[i - k] == s[i + k]) {
        k++;
    	}
    	d1[i] = k--;
    	if (i + k > r) {
       	 	l = i - k;
        	r = i + k;
    	}
	}
	vector<int> d2(n);
	for (int i = 0, l = 0, r = -1; i < n; i++) {
   		int k = (i > r) ? 0 : min(d2[l + r - i + 1], r - i + 1);
    	while (0 <= i - k - 1 && i + k < n && s[i - k - 1] == s[i + k]) {
        	k++;
    	}
    	d2[i] = k--;
   		if (i + k > r) {
        	l = i - k - 1;
        	r = i + k;
    	}
	}
	set<ll> st;
	long long ans = 0;
	for(ll i = n; i--;){
		for(ll j : vec[i]){
			st.erase(j);
		}
		vec[i].clear();
		st.insert(i);
		vec[i - d1[i]].pb(i);
		auto it = st.rbegin();
		while(it != st.rend()){
		ll t = (*it - i) * 2 + 1;
		if(t <= lcp[rnk[i] - 1]) break;;
		ll l = rnk[i], r = n + 1;
		while(r - l > 1){
			ll mid = (l + r) >> 1;
			if(get(rnk[i], mid) >= t) l = mid;
			else r = mid;
		}
		ans = max(ans, ((long long)t) * (r - rnk[i]));
		it++;
		}
	}
	st.clear();
	for(ll i = n - 1; i--;){
		for(ll j : vec[i]){
			st.erase(j);
		}
		if(d2[i + 1]) st.insert(i);
		if(d2[i + 1]) vec[i - d2[i + 1]].pb(i);
		if(st.empty()) continue;
		auto it = st.rbegin();
		while(it != st.rend()){
		ll t = (*it - i) * 2 + 2;
		if(t <= lcp[rnk[i] - 1]) break;
		ll l = rnk[i], r = n + 1;
		while(r - l > 1){
			ll mid = (l + r) >> 1;
			if(get(rnk[i], mid) >= t) l = mid;
			else r = mid;
		}
		ans = max(ans, ((long long)t) * (r - rnk[i]));
		it++;
		}
	}
	cout << ans;

    return 0;
}

• Subtask 1: 8 / 8
• Subtask 2: 15 / 15
• Subtask 3: 24 / 24
• Subtask 4: 26 / 26
• Subtask 5: 0 / 27