Submission #42049

#	Time	Username	Problem	Language	Result	Execution time	Memory
42049		cmaster	Palindromes (APIO14_palindrome)	C++14	0 / 100	1077 ms	4296 KiB

palindrome

#include <bits/stdc++.h>
/*#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/detail/standard_policies.hpp>*/
 
#define pb push_back
#define mp make_pair
#define sz(s) ((int)(s.size()))
#define all(s) s.begin(), s.end()
#define rep(i, a, n) for (int i = a; i <= n; ++i)
#define per(i, n, a) for (int i = n; i >= a; --i)
#define onlycin ios_base::sync_with_stdio(false); cin.tie(0) 
using namespace std;
// using namespace __gnu_pbds;
typedef long long ll;
typedef unsigned long long ull;
/*typedef tree<
pair < int, int >,
null_type,
less< pair < int, int > >,
rb_tree_tag,
tree_order_statistics_node_update>
ordered_set;*/
// find_by_order() order_of_key()
const int MAXN = (int)1e5+228;
const char nxtl = '\n';
const int mod = (int)1e9+7;
const double eps = (double)1e-7;
template<typename T> inline bool updmin(T &a, const T &b) {return a > b ? a = b, 1 : 0;}
template<typename T> inline bool updmax(T &a, const T &b) {return a < b ? a = b, 1 : 0;}

int n, suff[MAXN], c[MAXN], nc[MAXN], tmp[MAXN], cnt[MAXN], timer;
char s[MAXN];
int lcp[MAXN], pos[MAXN];

inline void calc() {
	rep(i, 1, max(n, 256)) cnt[i] += cnt[i - 1];
	per(i, max(n, 256), 0) cnt[i + 1] = cnt[i];
	cnt[0] = 0;
}

inline void SA() {
	memset(cnt, 0, sizeof cnt);
	s[n++] = (char)0;
	rep(i, 0, n - 1) cnt[s[i]]++;
	calc();
	rep(i, 0, n - 1) {
		suff[cnt[s[i]]++] = i;
	}
	c[suff[0]] = 0;
	rep(i, 1, n - 1) {
		if(s[suff[i]] == s[suff[i - 1]]) c[suff[i]] = c[suff[i - 1]];
		else c[suff[i]] = c[suff[i - 1]] + 1;
	}
	for(int len = 1; len <= n; len += len) {
		rep(i, 0, n - 1) tmp[i] = (suff[i] - len + n) % n;
		memset(cnt, 0, sizeof cnt);
		rep(i, 0, n - 1) cnt[c[suff[i]]]++;
		calc();
		rep(i, 0, n - 1) suff[cnt[c[tmp[i]]]++] = tmp[i];
		nc[suff[0]] = 0;
		rep(i, 1, n - 1) {
			pair < int, int > cur = { c[suff[i]], c[(suff[i] + len) % n] };
			pair < int, int > last = { c[suff[i - 1]], c[(suff[i - 1] + len) % n] };
			if(cur == last) nc[suff[i]] = nc[suff[i - 1]];
			else nc[suff[i]] = nc[suff[i - 1]] + 1;
		}
		rep(i, 0, n - 1) c[i] = nc[i];
	}
	n--;
	rep(i, 0, n - 1) suff[i] = suff[i + 1];
}

void build() {
	rep(i, 0, n - 1) pos[suff[i]] = i;
	int k = 0;
	rep(i, 0, n - 1) {
		if(k > 0) k--;
		if(pos[i] == n - 1) {
			k = 0;
			lcp[n - 1] = 0;
		}
		else {
			int j = suff[pos[i] + 1];
			while(k <= n && max(i + k, j + k) < n && s[(i + k) % n] == s[(j + k) % n]) k++;
			lcp[pos[i]] = k;
		}
	}
}
bool ok(int l, int r) {
	if(l > r) return 1;
	if(s[l] != s[r]) return 0;
	return ok(l+1, r-1);
}
int sv[MAXN];

int main() {
	#ifdef accepted
		freopen(".in", "r", stdin);
		freopen(".out", "w", stdout);
	#endif
	// onlycin;
	scanf("%s", s);
	n = strlen(s);
	SA();
	build();
	ll res = 0ll;
	rep(i, 0, n-1) cerr << suff[i] << ' ';
	cerr << nxtl;
	rep(i, 0, n-1) {
		int len = n-suff[i];
		while(!ok(suff[i], suff[i]+len-1)) len--;
		sv[i] = len;
		cerr << lcp[i] << ' ';
	}
	cerr << nxtl;
	rep(i, 0, n-1) {
		int l = i, kol = 1, r = i+1;
		while(l >= 0 && lcp[l] >= sv[i]) l--;
		while(r <= n-2 && lcp[r] >= sv[i]) r++;
		l++, r--;
		kol += r - l + 1;
		cerr << sv[i] << ' '<< l << ' '<< r << nxtl;
		updmax(res, sv[i] * 1ll * kol);
	}
	cout << res << nxtl;

	return 0;
}

Compilation message (stderr)

palindrome.cpp: In function 'void SA()':
palindrome.cpp:45:27: warning: array subscript has type 'char' [-Wchar-subscripts]
  rep(i, 0, n - 1) cnt[s[i]]++;
                           ^
palindrome.cpp:48:16: warning: array subscript has type 'char' [-Wchar-subscripts]
   suff[cnt[s[i]]++] = i;
                ^
palindrome.cpp: In function 'int main()':
palindrome.cpp:103:16: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%s", s);
                ^

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