[HDU 2594]Simpsons’ Hidden Talents[kmp求公共前後綴]

題意:

求兩個串s1, s2中s1的前綴與s2的後綴的最長公共部分.

思路:

next數組應用.

注意先判斷主串是否結束, 再判斷模式串是否結束. 1WA><

#include <cstring>
#include <cstdio>
#include <algorithm>
const int MAXN = 50005;
int next[MAXN],ans;
char s1[MAXN];
char s2[MAXN];
//15MS	492K
void prekmp()
{
    next[0] = -1;
    int j = -1;
    for(int i=1;s1[i];i++)
    {
        while(j!=-1 && s1[j+1]!=s1[i])    j = next[j];
        if(s1[j+1]==s1[i])    j++;
        next[i] = j;
    }
}
void kmp()
{
    int j=-1;
    ans = 0;
    for(int i=0;s2[i];i++)
    {
        while(j!=-1 && s1[j+1]!=s2[i])    j = next[j];
        if(s1[j+1]==s2[i])  j++;
        if(!s2[i+1])
        {
            ans = j+1;
            s1[ans] = '\0';
        }
        if(!s1[j+1])    j = next[j];
    }
}
int main()
{
    while(~scanf("%s",s1))
    {
        scanf("%s",s2);
        prekmp();
        kmp();
        if(ans)
            printf("%s %d\n",s1,ans);
        else
            printf("0\n");
    }
}