bzoj2160(manacher)

manacher複習

可以按照自己思路來寫

#include<cstdio>
#include<cstring>
#include<cmath>
#include<cstdlib>
#include<algorithm>
using namespace std;
typedef long long ll;
const ll mod=19930726;

int n,m,p[1000005];
ll k,f[1000005];
char s[1000005];

ll aa(ll a,ll b)
{
	ll ans=1;
	while (b)
	{
		if (b&1) ans=ans*a%mod;
		a=a*a%mod;
		b>>=1;
	}
	return ans;
}

int main()
{
	scanf("%d%lld",&n,&k);
	scanf("%s",s+1);
	s[0]='$';
	int id=0,mx=0;
	for (int i=1;i<=n;i++)
	{
		if (mx>i) p[i]=min(mx-i,p[id-(i-id)]);
		else p[i]=0;
		while (s[i+p[i]]==s[i-p[i]]) p[i]++;p[i]--;
		if (i+p[i]>mx) mx=i+p[i],id=i;
		
		f[1+p[i]*2]++;
	}
	for (int i=n;i>=1;i--) f[i]+=f[i+2];
	ll ans=1;
	for (int i=n;i>=1&&k;i--) if (i&1) 
	{
		ans=ans*aa(i,min(f[i],k))%mod;
		k-=min(f[i],k);
	}
	if (k) printf("-1");
	else printf("%lld",ans);
	return 0;
}