hdu -- 1867 A + B for you again (KMP)

#include<iostream>
using namespace std;
const int P=500010;
int fail[P];
char a[500010],b[500010];
char ans[2][1000010];
int kmp(char* str, char* pat,int w){
int i, j, k;
memset(fail, -1, sizeof(fail));
for (i = 1; pat[i]; ++i) {
for (k=fail[i-1]; k>=0 && pat[i]!=pat[k+1];
k=fail[k]);
if (pat[k + 1] == pat[i]) fail[i] = k + 1;
}
i = j = 0;
while( pat[j] )
{ // By Fandywang
if( pat[j] == str[i] ) ++i, ++j;
else if(j == 0)++i;//第一个字符匹配失败，从str下个字符开始
else j = fail[j-1]+1;

if(str[i]==0)
{
sprintf(ans[w],"%s",str);
strcat(ans[w],pat+j);
return i-j;
}
if(pat[j]==0)
j=0;
}
if( !pat[j] )
{
sprintf(ans[w],"%s",str);
strcat(ans[w],pat+j);
return i-j;
}
}

int main()
{
while (scanf("%s%s",a,b)!=EOF)
{
kmp(a,b,0);
kmp(b,a,1);
int len1=strlen(ans[0]);
int len2=strlen(ans[1]);
if(len1==len2)
strcmp(ans[0],ans[1])>0?printf("%s/n",ans[1]):printf("%s/n",ans[0]);
else
len2>len1?printf("%s/n",ans[0]):printf("%s/n",ans[1]);
}
}