Hdu 2594(KMP)

Hdu传送门
连接s1,s2, kmp求前缀和后缀(给了两个字符串，有时可以连接解题 )

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
using namespace std;
#define ms(i,j) memset(i, j, sizeof i);

const int MAXN = 50000 + 5;

char s1[MAXN*3], s2[MAXN];
int n1, n2, n, f[MAXN*3];

void init()
{
    n1 = strlen(s1), n2 = strlen(s2);
    n =  n1 + n2;
    for (int i=n1;i<n;i++)
    {
        s1[i] = s2[i-n1];
    }
}
void solve()
{
    f[0] = f[1] = 0;
    for (int i=1;i<n;i++)
    {
        int j = f[i];
        while (j && s1[i]!=s1[j]) j = f[j];
        f[i+1] = (s1[i]==s1[j]) ? (j+1) : (0);
    }
    int i = n;
    while (f[i])
    {
        if (f[i]<=min(n1,n2)) 
        {
            for (int j=0;j<f[i];j++) putchar(s1[j]);
            printf(" %d\n", f[i]);
            return ;
        } 
        i = f[i];
    }
    printf("%d\n", 0);
}
int main()
{
    while (scanf("%s%s", s1, s2)==2)
    {
        init();
        solve();
    }
    return 0;
}