KMP算法

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KMP板子

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/*
 * @Author: onlooker
 * @Date: 2020-03-07 11:28:45
 * @LastEditTime: 2020-09-06 10:42:32
 * @FilePath: \code\test.cpp
 */
#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define maxn 15
int nextt[maxn]={0};
void getnext(string b){
    nextt[0]=-1;
    int i=0,j=-1;
    int m=b.size();
    while(i<m){
        if(j==-1||b[i]==b[j]){
            i++;j++;
            nextt[i]=j;
        }
        else{
            j=nextt[j];
        }
    }
}
int kmp(string a,string b)
{
    int i=0,j=0;
    int n=a.size(),m=b.size();
    while(i<n&&j<m){
        if(a[i]==b[j]||j==-1){
            i++;j++;
        }
        else{
            j=nextt[j];
        }
    }
    if(j==m){
        return i-j;
    }
    else{
        return -1;
    }
}
int main()
{
    string a,b;
    cin>>a>>b;
    getnext(b);
    int ans=-1;
    ans=kmp(a,b);
    if(ans!=-1){
        cout<<"find from "<<ans<<" to "<<ans+b.size()-1<<endl;
    }
    else{
        cout<<"not found"<<endl;
    }
    return 0;
}