hdu 2203 親和串

思路：如果第一個串長度小於第二個就no 
將第一個串後面加上第一個串前x個字符 (x是第二個串的長度)；
因爲如果這樣還不能匹配就循環多少都不會匹配；

#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;
const int maxn = 200000;
char a[maxn], b[maxn];
int nextval[maxn];
int len1, len2;

void get_nextval()
{
    int i = 0, j = -1;
    nextval[i] = -1;
    while(i < len2)
    {
        if(j == -1 || b[i] == b[j])
        {
            if(b[++i] != b[++j]) nextval[i] = j;
            else nextval[i] = nextval[j];
        }
        else j = nextval[j];
    }
}

void kmp_search()
{
    get_nextval();
    int i = 0, j = 0;
    while(i < len1 && j < len2)
    {
        if(j == -1 || a[i] == b[j]) ++i, j++;
        else j = nextval[j];
    }
    if(j == len2) printf("yes\n");
    else printf("no\n");
}

int main()
{
    while(scanf("%s%s", a, b) != EOF)
    {
        len2 = strlen(b);
        len1 = strlen(a);
        if(len1 < len2)
        {
            printf("no\n");
            continue;
        }
        for(int i = 0; i < len2; i++)
            a[len1+i] = a[i];
        len1 += len2;
        kmp_search();
    }
}