Gym - 101164C - Castle KMP

题目链接：传送门

题解：

　　利用KMP的fail失配数组，快速找到当前后缀与前缀的公共前缀点

#include<bits/stdc++.h>
using namespace std;
#pragma comment(linker, "/STACK:102400000,102400000")
#define ls i<<1
#define rs ls | 1
#define pii pair<int,int>
#define MP make_pair
typedef long long LL;
typedef unsigned long long ULL;
const long long INF = 1e18+1LL;
const double pi = acos(-1.0);
const int N = 2e6+, M = 1e3+,inf = 2e9;

int fail[N],vis[N],n,Q,cnt,op[N],QQ[N];
char a[N],b[N],ch[N][];
int sum[N];
void build_fail() {
    memset(fail,-,sizeof(fail));
    int j = -;
    for(int i = ; i < cnt; ++i) {
        while(j!=-&&b[j+]!=b[i]) j = fail[j];
        if(b[j+] == b[i]) j++;
        fail[i] = j;
    }
}
int len[N];
int main() {
    scanf("%d%d",&n,&Q);
    scanf("%s",a);
    for(int i = ; i < n; ++i) b[i] = a[i];
    cnt = n;
    len[] = n;
    for(int i = ; i <= Q; ++i) {
        scanf("%d",&op[i]);
        len[i] = len[i-];
        if(op[i] == ) {
            scanf("%s",ch[i]);
            b[cnt++] = ch[i][];
            len[i]+=;
        }
        else if(op[i] == ) QQ[cnt-] = ;
    }
    build_fail();
    for(int i = ; i < cnt; ++i) {
        sum[i] = QQ[i];
        if(fail[i]!=-) {
            sum[i] += sum[fail[i]];
        }
    }
    int ccnt = n;
    for(int i = ; i <= Q; ++i) {
        if(op[i] == ) {
            ccnt++;
        }
        else if(op[i] == ) {
            vis[ccnt-] = ;
        }
        else if(op[i] == ) {
            int ret = ;
            if(vis[ccnt-]) ret = sum[ccnt-];
            else ret = sum[ccnt-] - QQ[ccnt-];
            printf("%d\n",ret);
        }
    }
    return ;
}