poj 2752 Seek the Name, Seek the Fame【KMP】

The little cat is so famous, that many couples tramp over hill and dale to Byteland, and asked the little cat to give names to their newly-born babies. They seek the name, and at the same time seek the fame. In order to escape from such boring job, the innovative little cat works out an easy but fantastic algorithm: 

Step1. Connect the father's name and the mother's name, to a new string S. 
Step2. Find a proper prefix-suffix string of S (which is not only the prefix, but also the suffix of S). 

Example: Father='ala', Mother='la', we have S = 'ala'+'la' = 'alala'. Potential prefix-suffix strings of S are {'a', 'ala', 'alala'}. Given the string S, could you help the little cat to write a program to calculate the length of possible prefix-suffix strings of S? (He might thank you by giving your baby a name:) 

The input contains a number of test cases. Each test case occupies a single line that contains the string S described above. 

Restrictions: Only lowercase letters may appear in the input. 1 <= Length of S <= 400000. 

For each test case, output a single line with integer numbers in increasing order, denoting the possible length of the new baby's name.

ababcababababcabab
aaaaa

2 4 9 18
1 2 3 4 5

大致题意：
给出一个字符串str，求出str中存在多少子串，使得这些子串既是str的前缀，又是str的后缀。从小到大依次输出这些子串的长度

解题思路：重在理解KMP算法中next数组的含义，递归求解

#include<cstdio>
#define maxn 400002
char str[maxn];
int next[maxn],len,s;
void GetNext(){
    int i=0,j=-1;
    next[0]=-1;
    while(str[i]){
        if(j==-1||str[i]==str[j]){
            ++i;++j;next[i]=j;
        }else j=next[j];
    }
    len=i;
}
void GetVal(int n){
    if(next[n]==0) return ;
    GetVal(next[n]);
    printf("%d ",next[n]);
}
int main(){
    while(scanf("%s",str)==1){
        GetNext();
        GetVal(len);
        printf("%d\n",len);
    }return 0;
}