字符串前后缀(包含拼接)

#include<cstring>
#include<iostream>
#include<string>
using namespace std;
int main()
{
	string s1,s2;
	char s[10000];

	while(cin >> s1 >> s2)
	{
		int flag = 0;
		int len = s1.size();
		if(s2.size() < len)
			len = s2.size() ;
		for(int i = 0;i< len;++i)
		{
			if(s1[i] == s2[i])
			{
				s[i] = s1[i];
			    	flag = 1;
			}
			else 
				break;
		}
		if(flag)
		     cout << "The common prefix is " << s << endl;
		else 
		     cout << "No common prefix" << endl;
	}
	return 0;
}

#include<cstdio>
#include<cstring>
using namespace std;
const int maxn=1e5+10;
void cal_next(char* str,int* next,int len)
{
    next[0]=next[1]=0;
    for(int i=1;i<len;++i)
    {
        int j=next[i];
        while(j&&str[i]!=str[j])
            j=next[j];
        next[i+1]=(str[j]==str[i])?j+1:0;
    }
}
int kmp(char *str,int slen,char *ptr,int plen)
{
   
    int next[maxn];
    cal_next(ptr,next,plen);

    int j=0;
    for(int i=0;i<slen;i++)
    {
        while(j&&ptr[j]!=str[i])
            j=next[j];
        if(ptr[j]==str[i])
            ++j;
    }
    return j;
}
char str[maxn],ptr[maxn],ans[maxn];
 
int main()
{
    while(scanf("%s%s",str,ptr)!=EOF){
        int plen=strlen(ptr),slen=strlen(str);
        int len=kmp(str,slen,ptr,plen);
      
        if(len==0)  printf("0\n");
        else{
            memset(ans,0,sizeof(ans));
            memcpy(ans,ptr,len*sizeof (char));
            printf("%s %d\n",ans,len);
        }
    }
    return 0;
}