【回文自动机】 BZOJ 2565 最长双回文串

通道

题意：求最长不相交双回文串

思路：dp1[i]表示[1,i]的回文串，dp2[i]表示[i+1,len]的回文串，ans=max(dp1[i]+dp2[i]);

代码：

#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

typedef long long ll;

const int MAX_N = 600005;
const int SIG = 26 ;
struct PTree {
    int nxt[MAX_N][SIG], fail[MAX_N], cnt[MAX_N], num[MAX_N], len[MAX_N], S[MAX_N];
    int last, n, p;
    int newNode (int l) {
        memset(nxt[p], 0, sizeof nxt[p]);
        cnt[p] = num[p] = 0;
        len[p] = l;
        return p++;
    }
    void init() {
        p = last = n = 0;
        newNode(0), newNode(-1);
        S[n] = -1;
        fail[0] = 1;
    }
    int getFail(int x) {
        while (S[n - len[x] - 1] != S[n]) x = fail[x];
        return x;
    }
    void add(int c, int pos, int *dp) {
        c -= 'a';
        S[++n] = c;
        int cur = getFail(last);
        if (!nxt[cur][c]) {
            int now = newNode(len[cur] + 2);
            fail[now] = nxt[getFail(fail[cur])][c];
            nxt[cur][c] = now;
            num[now] = num[fail[now]] + 1;
        }
        last = nxt[cur][c];
        ++cnt[last];
        dp[pos] = len[last];
    }    
    void count() {
        for (int i = p - 1; i >= 0; --i) cnt[fail[i]] += cnt[i];
    }
};

PTree T;
char s[MAX_N];
int dp1[MAX_N], dp2[MAX_N];

int main() {
    while (1 == scanf("%s", s)) {
        T.init();
        for (int i = 0; s[i]; ++i) T.add(s[i], i, dp1);
        T.init();
        int len = strlen(s);
        for (int i = len - 1; i >= 0; --i) T.add(s[i], len - 1 - i, dp2);
        int ans = 2; 
        for (int i = 0; i + 1 < len; ++i) {
            ans = max(ans, dp1[i] + dp2[len - i - 2]);
        }
        printf("%d\n", ans);
    } 
    return 0;
}