HDU 1358 Period (KMP)

#include <stdio.h>#include <string.h>int next[1000005];void build_next(char str2[]){int i=0,j=-1;next[0] = -1;while (str2[i]){if (j==-1 || str2[i] == str2[j]){i++;j++;// if (str2[i] != str2[j])// { next[i] = j;     //传说中的f[j]，储存前缀相同的最长最大值// }// else// next[i] = next[j];}elsej = next[j];}}// int KMP(int len1,int len2)// {//     build_next(len2);// int i=0,j=0,cnt;// // while (i < len1)// {// if (j==-1 || str1[i] == str2[j])// {// i++;// j++;// if(j==len2)// return i-len2+1;// }// else// j = next[j];// }// return -1;// }int main(){int N,n,m,i,k,t;//scanf("%d",&N);char str[1000005];k=1;while (~scanf("%d",&N),N){scanf("%s",&str);    build_next(str);printf("Test case #%d\n",k++);for (i=2;str[i-1];i++){            t= i-next[i];if (i%t==0 && i/t>1){printf("%d %d\n",i,i/t);}}// for (i=0;i<N;i++)// {// printf("%d",next[i]);// }putchar('\n');}return 0;}

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分析：此题目一开始真心没读懂，后来看别人的题解才知道题意。就是说从字符串的第二个开始，看前面是循环串吗，是的话就输出此时的位置，和循环串的周期，周期必须大于1

字符编号从0开始，那么if(i%(i-next[i])==0)，则i前面的
串为一个轮回串，其中轮回子串出现i/(i-next[i])次。有点推导公式的感觉

对KMP算法又进一步了解了

Period

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 3959    Accepted Submission(s): 1932

Problem 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 file 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

3aaa12aabaabaabaab0

 

Sample Output

Test case #12 23 3Test case #22 26 29 312 4