poj 2752 Seek the Name, Seek the Fame KMP

Seek the Name, Seek the Fame

Time Limit: 20 Sec  Memory Limit: 256 MB

题目连接

http://poj.org/problem?id=2752

Description

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:)

Input

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.

 

Output

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

 

Sample Input

ababcababababcabab
aaaaa

Sample Output

2 4 9 18
1 2 3 4 5

HINT

 

题意

 给你一个串，如果这个串存在一个长度为n的前缀串，和长度为n的后缀串，并且这两个串相等，则输出他们的长度n。求出所有的长度n。

题解：

KMP中的get_next()。对前缀函数next[]又有了进一步的理解，str[1]~~str[next[len]]中的内容一定能与str[1+len-next[len]]~~str[len]匹配（图1）。然后呢我们循环地利用next，由于next的性质，即在图2中若左红串与左绿串匹配，则左红串比与右绿串匹配，因为图1的左红串与右红串是完全相等的。可以保证，每一次得出的字串都能匹配到最后一个字母，也就是得到一个前缀等于后缀。只不过这个字符串的长度在不断地减小罢了。

(上图是转的某题解，讲的很清楚）

代码：

 

//qscqesze
#include <cstdio>
#include <cmath>
#include <cstring>
#include <ctime>
#include <iostream>
#include <algorithm>
#include <set>
#include <vector>
#include <sstream>
#include <queue>
#include <typeinfo>
#include <fstream>
#include <map>
#include <stack>
typedef long long ll;
using namespace std;
//freopen("D.in","r",stdin);
//freopen("D.out","w",stdout);
#define sspeed ios_base::sync_with_stdio(0);cin.tie(0)
#define maxn 500001
#define mod 10007
#define eps 1e-9
int Num;
char CH[20];
//const int inf=0x7fffffff;   //нчоч╢С
const int inf=0x3f3f3f3f;
/*

inline void P(int x)
{
    Num=0;if(!x){putchar('0');puts("");return;}
    while(x>0)CH[++Num]=x%10,x/=10;
    while(Num)putchar(CH[Num--]+48);
    puts("");
}
*/
inline ll read()
{
    int x=0,f=1;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
    return x*f;
}
inline void P(int x)
{
    Num=0;if(!x){putchar('0');puts("");return;}
    while(x>0)CH[++Num]=x%10,x/=10;
    while(Num)putchar(CH[Num--]+48);
    puts("");
}
//**************************************************************************************

string s;
int p[maxn];
int ans[maxn];
int main()
{
    while(cin>>s)
    {
        memset(ans,0,sizeof(ans));
        memset(p,0,sizeof(p));
        int len=s.size();
        p[0]=-1;
        int j=-1,i=0;
        while(i<len)
        {
            if(j==-1||s[i]==s[j])
            {
                i++,j++;
                p[i]=j;
            }
            else j=p[j];
        }
        int cnt=0;
        int t=p[len-1];
        while(t!=-1)
        {
            cout<<t<<endl;
            if(s[t]==s[len-1])ans[cnt++]=t+1;
            t=p[t];
        }
        for(int i=cnt-1;i>=0;i--)
            cout<<ans[i]<<" ";
        cout<<len<<endl;
    }
}