Submission #134937

#	Time	Username	Problem	Language	Result	Execution time	Memory
134937		wilwxk	Palindromes (APIO14_palindrome)	C++14	0 / 100	48 ms	7696 KiB

palindrome

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

const int MAXN=3e5+5;
const ll MOD=1e9+9;
const ll P=257;
char c[MAXN];
ll h[MAXN], rh[MAXN];
ll pot[MAXN];
int n;
ll respf=0;

ll ghash(int ini, int fim) {
	ll val=0;
	if(ini<=fim) {
		if(ini!=0) val=h[ini-1];
		val*=pot[fim-ini+1]; val%=MOD;
		val=h[fim]-val;
		while(val<0) val+=MOD;
	}
	else {
		if(ini!=n-1) val=rh[ini+1];
		val*=pot[ini-fim+1]; val%=MOD;
		val=rh[fim]-val;
		while(val<0) val+=MOD;
	}
	return val;
}

ll testa(int k) {
	if(k==0||k==n+1) return 0;
	if(k<0||k>n) return -1;
	int resp=0;
	// printf("testing %d\n", k);
	unordered_map<ll, int> mp;
	for(int i=k-1; i<n; i++) {
		int ind=i-k+1;
		ll val=ghash(ind, i);
		// printf("  %d: %lld %lld\n", i, val, ghash(i, ind));
		if(val==ghash(i, ind)) {
			mp[val]++;
			resp=max(resp, mp[val]);
		}
	}
	// printf("  testa %d >> %lld\n", k, k*(ll)resp);
	return (ll)resp*k;
}

void precalc() {
	pot[0]=1;
	for(int i=1; i<=n; i++) pot[i]=(pot[i-1]*P)%MOD;
	for(int i=0; i<n; i++) {
		if(i!=0) h[i]=(h[i-1]*P)%MOD;
		h[i]+=(c[i]-'a'); h[i]%=MOD;
	}
	for(int i=n-1; i>=0; i--) {
		if(i!=n-1) rh[i]=(rh[i+1]*P)%MOD;
		rh[i]+=(c[i]-'a'); rh[i]%=MOD;
	}
}

int main() {
	scanf(" %s", c); n=strlen(c);
	precalc();

	// for(int i=1; i<=n; i++) respf=max(respf, testa(i));

	int opt=-1;
	for(int i=n; i>0; i/=2) {
		// printf("testa %d // %d\n", i, opt);
		while(opt+i<=n&&(testa(opt+i-1)<=testa(opt+i)||testa(opt+i-1)<=testa(opt+i+1))) {
			opt+=i;
		}
	}
	// printf("opt %d\n", opt);
	respf=max(respf, testa(opt-2));
	respf=max(respf, testa(opt-1));
	respf=max(respf, testa(opt));
	respf=max(respf, testa(opt+1));
	respf=max(respf, testa(opt+2));

	printf("%lld\n", respf);
}

Compilation message (stderr)

palindrome.cpp: In function 'int main()':
palindrome.cpp:64:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf(" %s", c); n=strlen(c);
  ~~~~~^~~~~~~~~~

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