题目链接:http://poj.org/problem?id=2406
Description
Given two strings a and b we define a*b to be their concatenation. For example, if a = “abc” and b = “def” then a*b = “abcdef”. If we think of concatenation as multiplication, exponentiation by a non-negative integer is defined in the normal way: a^0 = “” (the empty string) and a^(n+1) = a*(a^n).
Input
Each test case is a line of input representing s, a string of printable characters. The length of s will be at least 1 and will not exceed 1 million characters. A line containing a period follows the last test case.
Output
For each s you should print the largest n such that s = a^n for some string a.
Sample Input
abcd aaaa ababab .
Sample Output
1 4 3
Hint
This problem has huge input, use scanf instead of cin to avoid time limit exceed.
Source
题意:
求最小子串的循环次数;
思路:(转)
KMP,next[]表示模式串如果第i位(设str[0]为第0位)与文本串第j位不匹配则要回到第next[i]位继续与文本串第j位匹配。则模式串第1位到next[n]与模式串第n-next[n]位到n位是匹配的。所以思路和上面一样,如果n%(n-next[n])==0,则存在重复连续子串,长度为n-next[n]。
例如:a b a b a b
next:-1 0 0 1 2 3 4
next[n]==4,代表着,前缀abab与后缀abab相等的最长长度,这说明,ab这两个字母为一个循环节,长度=n-next[n];
代码如下:
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
using namespace std;
#define MAXN 1000017
int next[MAXN];
int len;
void getnext( char T[])
{
int i = 0, j = -1;
next[0] = -1;
while(i < len)
{
if(j == -1 || T[i] == T[j])
{
i++,j++;
next[i] = j;
}
else
j = next[j];
}
}
int main()
{
char ss[MAXN];
int length;
while(~scanf("%s",ss))
{
if(ss[0] == '.')
break;
len = strlen(ss);
getnext(ss);
length = len - next[len];
if(len%length == 0)
printf("%d\n",len/length);
else
printf("1\n");
}
return 0;
}