HDU(1867)A + B for you again (KMP)

#include <iostream>
#include <stdio.h>
#include <string>
#include <string.h>
#include <algorithm>
#include <math.h>
#include <vector>
#include <map>
#include <queue>
#include <stack>
#include <stdlib.h>
using namespace std;
const int maxn = 100002;
char s1[maxn],s2[maxn];
int next[maxn];
void getNext(char *s){
    int j=0,k=-1;
    next[0]=-1;
    int len = strlen(s);
    while( j < len ){
        if(k == -1 || s[j] == s[k])
            next[++j] = ++k;
        else
            k = next[k];
    }
}
int kmp(char *s,char *pat){
    int i = 0,j = 0;
    int len1 = strlen(s);
    int len2 = strlen(pat);
    getNext(pat);
    while(i < len1 && j < len2){
        if( j == -1 || s[i] == pat[j]){
            ++i;
            ++j;
        }
        else j = next[j];
    }
    if( i >= len1 )
        return j;
    return 0;
}
int main(){
    while(scanf("%s%s",s1,s2)!=EOF){
        int ans1,ans2;
        ans2 = kmp(s1,s2);
        ans1 = kmp(s2,s1);
        if( ans1 == ans2)
            if(strcmp(s1,s2) < 0)
                printf("%s%s",s1,s2+ans2);
            else
                printf("%s%s",s2,s1+ans1);
        else if( ans2 > ans1 )
            printf("%s%s",s1,s2+ans2);
        else
            printf("%s%s",s2,s1+ans1);
        printf("\n");
    }
    return 0;
}