扩展kmp模板

参考博客: https://wenku.baidu.com/view/8e9ebefb0242a8956bece4b3.html

　　　　 http://www.cnblogs.com/Rlemon/archive/2013/06/26/3157574.html

代码:

#include <iostream>
#include <stdio.h>
#include <string.h>
using namespace std;

const int MAXN = 1e5 + 10;
char str1[MAXN], str2[MAXN]; //str1为主串,str2为模式串
int exnext[MAXN], extend[MAXN], n, m;

void get_exnext(void){
    exnext[0] = m;
    int j = 0, k = 1; //k是使p最大的i
    while(j + 1 < m && str2[j] == str2[j + 1]) j++;
    exnext[1] = j;
    for(int i = 2; i < m; i++){
        int p = exnext[k] + k - 1; //p为当前匹配最远的位置
        int l = exnext[i - k]; //[k,p]匹配[0,exnext[k]-1],所以[i,p]匹配[i-k,exnext[k]-1],[i-k,i-k+l]匹配[0,l]
        if(i + l < p + 1) exnext[i] = l;
        else{
            j = max(0, p - i + 1);
            while(i + j < m && str2[i + j] == str2[j]) j++;
            exnext[i] = j;
            k = i;
        }
    }
}

void ex_kmp(void){
    get_exnext();
    int j = 0, k = 0;
    while(j < n && j < m && str1[j] == str2[j]) j++;
    extend[0] = j;
    for(int i = 1; i < n; i++){
        int p = extend[k] + k - 1;
        int l = exnext[i - k];
        if(i + l < p + 1) extend[i] = l;
        else{
            j = max(0, p - i + 1);
            while(i + j < n && j < m && str1[i + j] == str2[j]) j++;
            extend[i] = j;
            k = i;
        }
    }
}

int main(void){
    scanf("%s%s", str1, str2);
    n = strlen(str1);
    m = strlen(str2);
    ex_kmp();
    for(int i = 0; i < m; i++){
        cout << exnext[i] << " ";
    }
    cout << endl;
    for(int i = 0; i < n; i++){
        cout << extend[i] << " ";
    }
    cout << endl;
    return 0;
}