HDU 2594 扩展kmp模板题

　题目大意： 

给定两个字符串，在第一个字符串中找到一个最大前缀作为第二个字符串的后缀

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <queue>
#include <climits>
#include <cmath>
#include <cstdlib>

using namespace std;

#define ll long long
#define N 1000100
char a[N] , b[N];
int _next[N] , extend[N] , len1 , len2;

void get_next(char *T){// _next[i]: 以第i位置开始的子串 与 T的公共前缀
     int i,length = strlen(T);
     _next[0] = length;
     for(i = 0;i<length-1 && T[i]==T[i+1]; i++);
          _next[1] = i;
          int a = 1;
          for(int k = 2; k < length; k++){
                  int p = a+_next[a]-1, L = _next[k-a];
                  if( (k-1)+L >= p ){
                       int j = (p-k+1)>0? (p-k+1) : 0;
                       while(k+j<length && T[k+j]==T[j]) j++;// 枚举(p+1，length) 与(p-k+1,length) 区间比较
                       _next[k] = j, a = k;
                  }
                  else _next[k] = L;
         }
}
void getextend(char *S,char *T){
    int maxl=max(len1 , len2);
    for(int i=0 ; i<=maxl ; i++) _next[i]=0;
    get_next(T);
    int Slen = strlen(S), Tlen = strlen(T), a = 0;
    int MinLen = Slen>Tlen?Tlen:Slen;
    while(a<MinLen && S[a]==T[a]) a++;
    extend[0] = a, a = 0;
    for(int k = 1; k < Slen; k++){
      int p = a+extend[a]-1, L = _next[k-a];
      if( (k-1)+L >= p ){
           int j = (p-k+1)>0? (p-k+1) : 0;
           while(k+j<Slen && j<Tlen && S[k+j]==T[j] ) j++;
           extend[k] = j;a = k;
      }
      else extend[k] = L;
    }
}


int main()
{
    #ifndef ONLINE_JUDGE
        freopen("a.in" , "r" , stdin);
    #endif
    while(~scanf("%s%s" , a , b))
    {
        getextend(b , a);
        len1 = strlen(a) , len2 = strlen(b);
        int ret = 0;
        for(int i=0 ; i<len2 ; i++)
            if(extend[i]>ret&&extend[i]+i==len2) ret = extend[i];
        if(!ret) puts("0");
        else{
            strncpy(a , b+(len2-ret) , ret);
            a[ret] = '';
            printf("%s %d
" , a, ret);
        }
    }
    return 0;
}