Submission #535116

#	Time	Username	Problem	Language	Result	Execution time	Memory
535116		getac	Palindromes (APIO14_palindrome)	C++14	47 / 100	616 ms	11636 KiB

palindrome

//InTheNameOfGOD
//PRS;)
#include<bits/stdc++.h>
#define rep(i, l, r) for(int i = l; i < r; ++i)
#define per(i, l, r) for(int i = r - 1; i >= l; --i)
#define Fast cin.tie(0) -> sync_with_stdio(0);
#define min(x, y) (x < y ? x : y)
#define max(x, y) (x > y ? x : y)
#define X first
#define Y second
typedef long long ll;
using namespace std;
typedef pair<int, pair<int, int>> pi;
#pragma GCC optimize("unroll-loops")
#pragma GCC target("avx2")
constexpr ll mod = 2e9 + 11;
constexpr int xn = 3e5 + 5;
ll h1[xn], h2[xn], p[xn];
int a[xn], t[xn];
char s[xn];
inline ll mk(ll x, ll y, int z)
{
	y = (y * p[z]) % mod, x -= y;
	return x < 0 ? x + mod : x;
}
inline int lcp(int x, int y)
{
	int l = 1, r = min(t[x], t[y]) + 1;
	while(l < r)
	{
		int md = l + r >> 1;
		mk(h1[x + md], h1[x], md) == mk(h1[y + md], h1[y], md) ? l = md + 1 : r = md;
	}
	return l - 1;
}
inline bool cmp(int x, int y)
{
	int z = lcp(x, y);
	if(t[y] <= z) return 0;
	if(t[x] <= z) return 1;
	return s[x + z] < s[y + z];
}
int main()
{
	Fast
	scanf("%s", &s);
	int n = strlen(s);
	h1[0] = h2[n] = 0, p[0] = 1;
	rep(i, 0, n) h1[i + 1] = (h1[i] * 27 + s[i] - 'a' + 1) % mod;
	per(i, 0, n) h2[i] = (h2[i + 1] * 27 + s[i] - 'a' + 1) % mod;
	rep(i, 1, n + 1) p[i] = (p[i - 1] * 27) % mod;
	ll ans = 1;
	rep(i, 0, n)
	{
		int l = 2, r = min(n - i, i + 1) + 1;
		while(l < r)
		{
			int md = l + r >> 1;
			mk(h1[i + md], h1[i], md) == mk(h2[i - md + 1], h2[i + 1], md) ? l = md + 1 : r = md;
		}
		t[i] = l - 1;
		ans = max(ans, (t[i] << 1) - 1);
	}
	rep(i, 0, n) a[i] = i;
	sort(a, a + n, cmp);
	vector<pi> v;
	rep(i, 1, n)
	{
		int e = lcp(a[i - 1], a[i]), prs = 0;
		while(!v.empty() && v.back().X >= e)
		{
			pi j = v.back();
			v.pop_back();
			if(j.X > e) ans = max(ans, 1ll * ((j.X << 1) - 1) * (i - j.Y.X));
		}
		if(!v.empty()) prs = v.back().Y.Y;
		v.push_back({e, {prs, i}});
	}
	rep(i, 0, n)
	{
		int l = 1, r = min(n - i, i) + 1;
		while(l < r)
		{
			int md = l + r >> 1;
			mk(h1[i + md], h1[i], md) == mk(h2[i - md], h2[i], md) ? l = md + 1 : r = md;
		}
		t[i] = l - 1;
		ans = max(ans, t[i] << 1);
	}
	sort(a, a + n, cmp);
	for(pi i : v) ans = max(ans, 1ll * ((i.X << 1) - 1) * (n - i.Y.X));
	v.clear();
	rep(i, 1, n)
	{
		int e = lcp(a[i - 1], a[i]), prs = 0;
		while(!v.empty() && v.back().X >= e)
		{
			pi j = v.back();
			v.pop_back();
			if(j.X > e) ans = max(ans, 1ll * (j.X << 1) * (i - j.Y.X));
		}
		if(!v.empty()) prs = v.back().Y.Y;
		v.push_back({e, {prs, i}});
	}
	for(pi i : v) ans = max(ans, 1ll * (i.X << 1) * (n - i.Y.X));
	printf("%d\n", ans);
}

Compilation message (stderr)

palindrome.cpp: In function 'int lcp(int, int)':
palindrome.cpp:31:14: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   31 |   int md = l + r >> 1;
      |            ~~^~~
palindrome.cpp: In function 'int main()':
palindrome.cpp:46:10: warning: format '%s' expects argument of type 'char*', but argument 2 has type 'char (*)[300005]' [-Wformat=]
   46 |  scanf("%s", &s);
      |         ~^   ~~
      |          |   |
      |          |   char (*)[300005]
      |          char*
palindrome.cpp:58:15: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   58 |    int md = l + r >> 1;
      |             ~~^~~
palindrome.cpp:84:15: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   84 |    int md = l + r >> 1;
      |             ~~^~~
palindrome.cpp:106:11: warning: format '%d' expects argument of type 'int', but argument 2 has type 'll' {aka 'long long int'} [-Wformat=]
  106 |  printf("%d\n", ans);
      |          ~^     ~~~
      |           |     |
      |           int   ll {aka long long int}
      |          %lld
palindrome.cpp:46:7: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   46 |  scanf("%s", &s);
      |  ~~~~~^~~~~~~~~~

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