计蒜客 2018南京网络赛 I Skr ( 回文树 )

#include<bits/stdc++.h>
#define LL long long
#define ULL unsigned long long

#define scl(i) scanf("%lld", &i)
#define scll(i, j) scanf("%lld %lld", &i, &j)
#define sclll(i, j, k) scanf("%lld %lld %lld", &i, &j, &k)
#define scllll(i, j, k, l) scanf("%lld %lld %lld %lld", &i, &j, &k, &l)

#define scs(i) scanf("%s", i)
#define sci(i) scanf("%d", &i)
#define scd(i) scanf("%lf", &i)
#define scIl(i) scanf("%I64d", &i)
#define scii(i, j) scanf("%d %d", &i, &j)
#define scdd(i, j) scanf("%lf %lf", &i, &j)
#define scIll(i, j) scanf("%I64d %I64d", &i, &j)
#define sciii(i, j, k) scanf("%d %d %d", &i, &j, &k)
#define scddd(i, j, k) scanf("%lf %lf %lf", &i, &j, &k)
#define scIlll(i, j, k) scanf("%I64d %I64d %I64d", &i, &j, &k)
#define sciiii(i, j, k, l) scanf("%d %d %d %d", &i, &j, &k, &l)
#define scdddd(i, j, k, l) scanf("%lf %lf %lf %lf", &i, &j, &k, &l)
#define scIllll(i, j, k, l) scanf("%I64d %I64d %I64d %I64d", &i, &j, &k, &l)

#define lson l, m, rt<<1
#define rson m+1, r, rt<<1|1
#define lowbit(i) (i & (-i))
#define mem(i, j) memset(i, j, sizeof(i))

#define fir first
#define sec second
#define VI vector<int>
#define ins(i) insert(i)
#define pb(i) push_back(i)
#define pii pair<int, int>
#define VL vector<long long>
#define mk(i, j) make_pair(i, j)
#define all(i) i.begin(), i.end()
#define pll pair<long long, long long>

#define _TIME 0
#define _INPUT 0
#define _OUTPUT 0
clock_t START, END;
void __stTIME();
void __enTIME();
void __IOPUT();
using namespace std;
const LL mod = 1e9 + 7;

LL pow_mod(LL a, LL b)
{
    a %= mod;
    LL ret = 1;
    while(b){
        if(b & 1) ret = ret * a % mod;
        a = a * a % mod;
        b >>= 1;
    }return ret;
}

const int maxn = 2000000 + 10;
const int N = 15 ;

struct Palindromic_Tree {
    int next[maxn][N] ;//next指针，next指针和字典树类似，指向的串为当前串两端加上同一个字符构成
    int fail[maxn] ;//fail指针，失配后跳转到fail指针指向的节点
    int cnt[maxn] ;
    int num[maxn] ;
    int len[maxn] ;//len[i]表示节点i表示的回文串的长度
    int S[maxn] ;//存放添加的字符
    int last ;//指向上一个字符所在的节点，方便下一次add
    int n ;//字符数组指针
    int tot ;//节点指针

    LL val[maxn];

    int newnode ( int l ) {//新建节点
        for ( int i = 0 ; i < N ; ++ i ) next[tot][i] = 0 ;
        cnt[tot] = 0 ;
        num[tot] = 0 ;
        val[tot] = 0LL;
        len[tot] = l ;
        return tot ++ ;
    }

    void init () {//初始化
        tot = 0 ;
        newnode (  0 ) ;
        newnode ( -1 ) ;
        last = 0 ;
        n = 0 ;
        S[n] = -1 ;//开头放一个字符集中没有的字符，减少特判
        fail[0] = 1 ;
    }

    int get_fail ( int x ) {//和KMP一样，失配后找一个尽量最长的
        while ( S[n - len[x] - 1] != S[n] ) x = fail[x] ;
        return x ;
    }

    void add ( int c ) {
        c -= ‘0‘ ;
        S[++ n] = c ;
        int cur = get_fail ( last ) ;//通过上一个回文串找这个回文串的匹配位置
        if ( !next[cur][c] ) {//如果这个回文串没有出现过，说明出现了一个新的本质不同的回文串
            int now = newnode ( len[cur] + 2 ) ;//新建节点
            fail[now] = next[get_fail ( fail[cur] )][c] ;//和AC自动机一样建立fail指针，以便失配后跳转
            next[cur][c] = now ;
            num[now] = num[fail[now]] + 1 ;
        }
        int pre = cur;
        last = next[cur][c] ;

        //c*10^(len[pre]+1) + val[pre]*10 + c
        if(len[pre] == -1) val[last] = c;
        else val[last] = ( (val[pre] * 10) % mod + (c * pow_mod(10, len[pre]+1) % mod ) % mod + c ) % mod;

        cnt[last] ++ ;
    }

    void count () {
        for ( int i = tot - 1 ; i >= 0 ; -- i ) cnt[fail[i]] += cnt[i] ;
        //父亲累加儿子的cnt，因为如果fail[v]=u，则u一定是v的子回文串！
    }
}PAM;

char s[maxn];
int main(void){__stTIME();__IOPUT();

    PAM.init();

    scanf("%s", s);

    int len = strlen(s);

    for(int i=0; i<len; i++) PAM.add(s[i]);

    PAM.count();

    LL ans = 0;
    for(int i=2; i<PAM.tot; i++)
        ans = (ans + PAM.val[i]) % mod;

    printf("%lld\n", ans);



__enTIME();return 0;}


void __stTIME()
{
    #if _TIME
        START = clock();
    #endif
}

void __enTIME()
{
    #if _TIME
        END = clock();
        cerr<<"execute time = "<<(double)(END-START)/CLOCKS_PER_SEC<<endl;
    #endif
}

void __IOPUT()
{
    #if _INPUT
        freopen("in.txt", "r", stdin);
    #endif
    #if _OUTPUT
        freopen("out.txt", "w", stdout);
    #endif
}