KMP算法

#include <bits/stdc++.h>

using namespace std;

typedef long long LL;
int next[10000];
void prekmp(char x[], int m) {//这一步坑爹，next数组为一张部分匹配表
    int i = 0, j = -1;
     next[0] = -1;
     while(i < m) {
         while(j != -1  && x[i] != x[j] ) j = next[j];
         if(x[++i] == x[++j]) next[i] = next[j];
         else next[i] = j;
     }
}
int KMP(char x[], int m, char y[], int n) {这个还好理解
    int i = 0, j = 0;
    int ans = 0;
    prekmp(x, m);
    while(i < n) {
        while(j != -1 && x[j] != y[i]) j = next[j];//用到next数组，不用一个一个对比，直接用放在next的位置，位置文章最后有解释
         i++; j++;
        if(j >= m) {
            ans++;
            j = next[j];
        }
    }
    return ans;
}
int main() {
    //freopen("in.txt","r",stdin);
    //freopen("out.txt,"w",stdout");
    ios_base::sync_with_stdio(0);cin.tie();
     char x[10000], y[10000];
     scanf("%s%s",y,x);
     int m = strlen(x); 
     int n = strlen(y);
     cout << endl;
     cout << KMP(x, m, y, n) << endl;
     for(int i = 0; i < m; i++)//print value
         cout << next[i] << "" ;
     cout << endl;
     return 0;
}