HDU 1358 Period 求周期串（kmp）

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Period

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 2458    Accepted Submission(s): 1218

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

给你一个字符串，让你求它所有的前缀能否形成周期串，如果可以输出周期串的循环次数，要求次数大于1.

kmp中的未优化的nex数组存的是字符串的前后缀最大匹配情况，可以根据这个求出每个前缀的最小周期的长度t，t=i-next[i]，如果i%t==0，说明能够形成周期串，那么周期串的循环次数就是i/t.

//125MS5144K#include<stdio.h>#include<string.h>char pattern[1000007];int next[1000007],m;void pre(){int i = 0, j = -1;next[0] = -1;while(i != m){if(j == -1 || pattern[i] == pattern[j])next[++i] = ++j;elsej = next[j];}}int main(){    int cas=1;    while(scanf("%d",&m),m)    {        memset(next,0,sizeof(next));        scanf("%s",pattern);        pre();        printf("Test case #%d\n",cas++);        for(int i=1;i<=m;i++)        {            int len=i-next[i];//求第i个字符的最小周期            if(i%len==0&&i/len!=1)//如果能够形成周期串且长度>1                printf("%d %d\n",i,i/len);//输出循环次数        }        printf("\n");    }    return 0;}