扩展kmp

扩展kmp本质还是kmp

有点类似马拉车

就是改变next数组含义为与记录与自身最长的公共前缀的长度（这个也用扩展kmp求）

#include<iostream>
#include<cstdio>
#include<cmath>
#include<string.h>
#include<cstring>
using namespace std;
const int maxn = 1e6+1000;
char x[maxn];

int m;

char s[maxn];
char a[maxn];
char b[maxn];

int knext[maxn],extend[maxn];
void pre_ekmp(char x[],int m,int knext[]){
    knext[0] = m;
    int j = 0;
    while(j+1<m && x[j]==x[j+1])j++;
    knext[1] = j;
    int k = 1;
    for(int i = 2;i<m;++i){
        int p = knext[k]+k-1;
        int L = knext[i-k];
        if(i+L<p+1)knext[i] = L;
        else{
            j = max(0,p-i+1);
            while(i+j<m&&x[i+j]==x[j])j++;
            knext[i] = j;
            k = i;
        }

    }
}
void EKmp(char x[],int m, char y[], int n, int knext[], int extend[]){
    pre_ekmp(x,m,knext);
    int j = 0;
    while(j < n && j < m && x[j] == y[j])j++;
    extend[0] = j;
    int k = 0;
    for(int i = 1;i < n; ++i){
        int p = extend[k] + k - 1;
        int L = knext[i - k];
        if(i+L < p+1) extend[i] = L;
        else{
            j = max(0,p-i+1);
            while(i + j < n && j < m && y[i+j] == x[j] )j++;
            extend[i] = j;
            k = i;
        }
    }
}

int main(){
    int t;

        scanf("%s%s",a,b);
        int lena = strlen(a);
        int lenb = strlen(b);
        
        EKmp(b,lenb,a,lena,knext,extend);//求a的每一个后缀与b的最长公共前缀
        for(int i =0; i < lenb; ++i){
            printf("%d ",knext[i]);
        }

        printf("\n");

        for(int i =0; i < lena; ++i){
            printf("%d ",extend[i]);
        }

        printf("\n");

}