BZOJ 3620: 似乎在梦中见过的样子 [KMP 暴力]

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
using namespace std;
typedef long long ll;
const int N=15005,MOD=1e9+7;
int n,k,ans;
char s[N];
int fail[N],sum[N];
void KMP(char s[],int n){
    fail[1]=0;
    for(int i=2;i<=n;i++){
        int j=fail[i-1];
        while(j&&s[i]!=s[j+1]) j=fail[j];
        fail[i]=s[i]==s[j+1]?j+1:0;
    }
    int j=0;
    for(int i=2;i<=n;i++){
        while(j&&s[i]!=s[j+1]) j=fail[j];
        if(s[i]==s[j+1]) j++;
        while((j<<1)>i-1) j=fail[j];
        ans+=j>=k;
    }
}
int main(){
    freopen("in","r",stdin);
    scanf("%s%d",s+1,&k);
    n=strlen(s+1);
    int _=n-(k<<1);
    for(int i=0;i<_;i++) KMP(s+i,n-i);
    printf("%d",ans);
}