poj 1961 Period (kmp next 数组的应用)

http://poj.org/problem?id=1961

Period

Time Limit: 3000MS		Memory Limit: 30000K
Total Submissions: 10855		Accepted: 4995

Description

For each prefix of a given string S with N characters (each character has an ASCII code between 97 and 126, inclusive), we want to know whether the prefix is a periodic string. That is, for each i (2 <= i <= N) we want to know the largest K > 1 (if there is one) such that the prefix of S with length i can be written as A^K ,that is A concatenated K times, for some string A. Of course, we also want to know the period K.

Input

The input consists of several test cases. Each test case consists of two lines. The first one contains N (2 <= N <= 1 000 000) – the size of the string S.The second line contains the string S. The input file ends with a line, having the number zero on it.

Output

For each test case, output "Test case #" and the consecutive test case number on a single line; then, for each prefix with length i that has a period K > 1, output the prefix size i and the period K separated by a single space; the prefix sizes must be in increasing order. Print a blank line after each test case.

Sample Input

3
aaa
12
aabaabaabaab
0

Sample Output

Test case #1
2 2
3 3

Test case #2
2 2
6 2
9 3
12 4

此题考查对kmp中next数组的理解与应用
代码：

 1 #include<iostream>
 2 #include<string.h>
 3 #include<stdio.h>
 4 using namespace std;
 5 #define MAX 1000000
 6 void get_next(char *str,int *next)
 7 {
 8     int i=0,j=-1;
 9     int tlen=strlen(str);
10     next[0]=-1;
11     while(i<tlen)
12     {
13         if(j==-1||str[i]==str[j])
14         {
15             i++;
16             j++;
17             if(i%(i-j)==0&&i/(i-j)>1)  //主要代码
18                 printf("%d %d\n",i,i/(i-j));
19             if(str[i]!=str[j])
20                 next[i]=j;
21             else
22                 next[i]=next[j];
23         }
24         else
25             j=next[j];
26     }
27 }
28 char str[MAX+10];
29 int next[MAX+10];
30 int main()
31 {
32     int t=1,n;
33     while(~scanf("%d",&n)&&n)
34     {
35         scanf("%s",str);
36         printf("Test case #%d\n",t++);
37         get_next(str,next);
38         printf("\n");
39     }
40     return 0;
41 }