Submission #368175

#	Time	Username	Problem	Language	Result	Execution time	Memory
368175		AriaH	Palindromes (APIO14_palindrome)	C++11	100 / 100	865 ms	29388 KiB

palindrome

/** Im the best because i work as hard as i possibly can **/
 
#include <bits/stdc++.h>
using namespace std;
 
typedef long long                   ll;
typedef long double                 ld;
typedef pair<int,int>               pii;
typedef pair<ll,ll>                 pll;
#define all(x)                      (x).begin(),(x).end()
#define F                           first
#define S                           second
#define Mp                          make_pair
#define fast_io                     ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define file_io                     freopen("in.txt" , "r+" , stdin) ; freopen("out.txt" , "w+" , stdout);
#define endl                        "\n"
 
const int N = 1e6 + 10;
const ll mod = 884577481;
const ll mod2 = 998244353;
const ll inf = 8e18;
const int LOG = 22;
const ll base = 609859;
 
string s;
 
char C[N];
 
int n, rnk[N], SA[N], tmp[N], Cnt[N], lcp[N], seg[N << 2];
 
ll pw[N], hshL[N], hshR[N];

inline void BuildSuffixArray(){
    assert((s[0] == '$') && (n + 1 == (int)s.size()));
    int _pw = 0;
    iota(SA + 1, SA + n + 1, 1), SA[0] = n + 1;
    for(int i = 1; i <= n; i ++) rnk[i] = s[i];
    int _Max = 'z', p = 1, k;
    for(_pw = 0; p < n; _pw ++){
        k = ((1LL << _pw) >> 1), p = 1;
        for(int i = n - k + 1; i <= n; i ++){
            tmp[p ++] = i;
        }
        for(int i = 1; i <= n; i ++){
            if(SA[i] > k) tmp[p ++] = SA[i] - k;
        }
        for(int i = 0; i <= _Max; i ++) Cnt[i] = 0;
        for(int i = 1; i <= n; i ++) Cnt[rnk[i]] ++;
        for(int i = 1; i <= _Max; i ++){
            Cnt[i] += Cnt[i - 1];
        }
        for(int i = n; i; i --){
            SA[Cnt[rnk[tmp[i]]] --] = tmp[i];
        }
        swap(rnk, tmp);
        rnk[SA[1]] = p = 1;
        for(int i = 2; i <= n; i ++){
            if(tmp[SA[i - 1]] != tmp[SA[i]] || SA[i - 1] + k > n || tmp[SA[i - 1] + k] != tmp[SA[i] + k]){
                p ++;
            }
            rnk[SA[i]] = p;
        }
        _Max = p;
    }
    SA[0] = n + 1;
}
inline void BuildLcpTable(){
    assert((s[0] == '$') && (n + 1 == (int)s.size()));
    for(int i = 1, k = 0; i <= n; i ++){
        if(rnk[i] == n) continue;
        if(k) k --;
        while(s[i + k] == s[SA[rnk[i] + 1] + k]){
            k ++;
        }
        lcp[rnk[i] + 1] = k;
    }
}

inline ll baze(int l, int r)
{
	return (hshL[r] - (hshL[l - 1] * pw[r - l + 1] % mod) + mod) % mod;
}
 
inline ll baze2(int l, int r)
{
	return (hshR[l] - (hshR[r + 1] * pw[r - l + 1] % mod) + mod) % mod;
}
 
void build(int v = 1, int tl = 1, int tr = n)
{
	if(tl == tr)
	{
		seg[v] = lcp[tl];
		return;
	}
	int mid = (tl + tr) >> 1;
	build(v << 1, tl, mid), build(v << 1 | 1, mid + 1, tr);
	seg[v] = min(seg[v << 1], seg[v << 1 | 1]);
}
 
int find_nxt(int p, int x, int v = 1, int tl = 1, int tr = n)
{
	if(p > n) return n + 1;
	if(tr < p) return -1;
	if(seg[v] >= x)
	{
		if(tr == n) return n + 1;
		return -1;
	}
	if(tl == tr) return tl;
	int mid = (tl + tr) >> 1;
	int cu = find_nxt(p, x, v << 1, tl, mid);
	if(cu == -1) cu = find_nxt(p, x, v << 1 | 1, mid + 1, tr);
	return cu;
}
 
int find_prv(int p, int x, int v = 1, int tl = 1, int tr = n)
{
	if(tl > p) return -1;
	if(seg[v] >= x)
	{
		if(tl == 1) return 0;
		return -1;
	}
	if(tl == tr) return tl;
	int mid = (tl + tr) >> 1;
	int cu = find_prv(p, x, v << 1 | 1, mid + 1, tr);
	if(cu == -1) cu = find_prv(p, x, v << 1, tl, mid);
	return cu;
}
 
ll calc(int l, int r)
{
	int sz = r - l + 1, id = rnk[l];
	int L = find_prv(id, sz);
	int R = find_nxt(id + 1, sz);
	return R - L;
}
 
int main()
{
	scanf("%s", C);
	n = strlen(C);
	s = C;
	s = "$" + s;
	pw[0] = 1;
	for(int i = 1; i < N; i ++) pw[i] = pw[i - 1] * base % mod;
	for(int i = 1; i <= n; i ++)
	{
		hshL[i] = (hshL[i - 1] * base + s[i] - 'a' + 1) % mod;
	}
	for(int i = n; i >= 1; i --)
	{
		hshR[i] = (hshR[i + 1] * base + s[i] - 'a' + 1) % mod;
	}
	BuildSuffixArray();
	BuildLcpTable();
	build();
	ll tot = 0;
	for(int i = 1; i <= n; i ++)
	{
		int d = 0, up = min(i - 1, n - i) + 1;
		while(up - d > 1)
		{
			int mid = (up + d) >> 1;
			if(baze(i, i + mid) == baze2(i - mid, i)) d = mid;
			else up = mid;
		}
		tot = max(tot, calc(i - d, i + d) * (2 * d + 1));
	}
	for(int i = 1; i < n; i ++)
	{
		if(s[i] != s[i + 1]) continue;
		int d = 0, up = min(i - 1, n - i - 1) + 1;
		while(up - d > 1)
		{
			int mid = (up + d) >> 1;
			if(baze(i + 1, i + 1 + mid) == baze2(i - mid, i)) d = mid;
			else up = mid;
		}
		tot = max(tot, calc(i - d, i + d + 1) * (2 *  d + 2));
	}
	printf("%lld", tot);
	return 0;
}

Compilation message (stderr)

palindrome.cpp: In function 'int main()':
palindrome.cpp:142:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  142 |  scanf("%s", C);
      |  ~~~~~^~~~~~~~~

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