bzoj4044: [Cerc2014] Virus synthesis（回文自动机）

题目
学习博客
题解

#include<bits/stdc++.h>
using namespace std;
const int N=100002;
int mp[99],ans,T,f[N],fail[N],ch[N][4],sz,q[N],h,t,len[N],s[N],n,las[N],last,u,v,i;
char c;
void init(int u,int l,int f){
	ch[u][0]=ch[u][1]=ch[u][2]=ch[u][3]=0;
	len[u]=l,fail[u]=f;
}
int F(int u){for (;s[n-len[u]-1]!=s[n];u=fail[u]);return u;}
void extend(int c){
	int u=F(last);
	if (!ch[u][c]){
		int v=++sz;
		init(ch[u][c]=v,len[u]+2,ch[F(fail[u])][c]);
		if (len[v]<=2) las[v]=fail[v];
		else{
			int x=las[u];
			for (;s[n-len[x]-1]!=s[n] || (len[x]+2<<1)>len[v];x=fail[x]);
			las[v]=ch[x][c];
		}
	}
	last=ch[u][c];
}
void build(){
	last=n=0,sz=1;
	for (;c<'A' || c>'Z';c=getchar());
	for (;'A'<=c && c<='Z';c=getchar()) extend(s[++n]=mp[c]);
}
int main(){
	mp['C']=1,mp['G']=2,mp['T']=3;s[0]=-1;
	for (scanf("%d",&T);T--;){
		init(0,0,1),init(1,-1,0);
		f[0]=fail[0]=1,fail[1]=0;
		build();
		for (i=1;i<=sz;i++)
			if (len[i]&1) f[i]=len[i];
		h=0,t=1,ans=n;
		while (h<t){
			u=q[h++];
			for (i=0;i<4;i++)
				if (v=ch[u][i]){
					f[v]=min(f[u]+1,len[v]/2+1+f[las[v]]-len[las[v]]);
					ans=min(ans,n+f[v]-len[v]);
					q[t++]=v;
				}
		}
		printf("%d\n",ans);
	}
}