BZOJ 3676: [Apio2014]回文串 回文自动机

Code:

#include <cstdio>
#include <cstring>
#include <algorithm> 
#define ll long long
#define N 300005 
#define maxn 300005 
#define setIO(s) freopen(s".in","r",stdin) 
using namespace std;
int str[maxn],n; 
char s[maxn]; 
ll ans;
struct PAM{
    int fail[N],cnt[N],len[N],ch[N][30],last,tot; 
    void init(){
        str[0] = -1,fail[0] = 1,last = 0;
        len[0] = 0,len[1] = -1, tot = 1; 
    }
    int newnode(int x) {
        len[++tot] = x; 
        return tot; 
    }
    int getfail(int x,int nn){
        while(str[nn - len[x] - 1] != str[nn]) x = fail[x]; 
        return x; 
    }
    void ins(int c,int i) {
        int p = getfail(last,i);
        if(!ch[p][c]) {
            int q = newnode(len[p] + 2); 
            fail[q] = ch[getfail(fail[p],i)][c];
            ch[p][c] = q; 
        }
        ++cnt[last = ch[p][c]]; 
    }
    void solve(){
        for(int i = tot;i >= 1; --i) {
            ans = max(ans,(ll)cnt[i]*len[i]); 
            cnt[fail[i]] += cnt[i]; 
        }
    }
}T; 
int main(){
    //setIO("input"); 
    scanf("%s",s + 1),n = strlen(s + 1),T.init(); 
    for(int i = 1;i <= n; ++i) str[i] = s[i] - 'a'; 
    for(int i = 1;i <= n; ++i) T.ins(str[i],i); 
    T.solve(); 
    printf("%lld\n",ans);
    return 0;
}

标签：cnt,ch,tot,int,len,Apio2014,fail,3676,回文
来源： https://www.cnblogs.com/guangheli/p/10361322.html