题意是求第一个字符的前缀和后一个字符串的后缀最大的公共序列，并输出。。。
将两个字符串合并，求出kmp中的next数组就行，但要注意不要大于某个字符串的长度；
#include <stdio.h>
#include <string.h>
const int N = 50005;
#define min(a,b) ((a)<(b)?(a):(b))
char s1[N], s2[N], s3[N * 2];
int next[N * 2];
void get_next(char *seq, int m) {
next[0] = -1;
int j = next[0];
for (int i = 1; i < m; i++) {
while (j >= 0 && seq[i] != seq[j + 1]) j = next[j];
if (seq[i] == seq[j + 1]) j++;
next[i] = j;
}
}
int main() {
while (~scanf("%s%s", s1, s2)) {
int len1 = strlen(s1), len2 = strlen(s2);
strcpy(s3, s1); strcpy(s3 + len1, s2);
int len3 = strlen(s3);
get_next(s3, len3);
int ans = min(min(len1, len2), next[len3 - 1] + 1);
for (int i = 0; i < ans; i++)
printf("%c", s1[i]);
if (ans) printf(" ");
printf("%d\n", ans);
}
return 0;
}