Uva455

Periodic Strings UVA - 455

A character string is said to have period k if it can be formed by concatenating one or more repetitions of another string of length k. For example, the string ”abcabcabcabc” has period 3, since it is formed by 4 repetitions of the string ”abc”. It also has periods 6 (two repetitions of ”abcabc”) and 12 (one repetition of ”abcabcabcabc”). Write a program to read a character string and determine its smallest period. Input The first line oif the input file will contain a single integer N indicating how many test case that your program will test followed by a blank line. Each test case will contain a single character string of up to 80 non-blank characters. Two consecutive input will separated by a blank line. Output An integer denoting the smallest period of the input string for each input. Two consecutive output are separated by a blank line. Sample Input 1
HoHoHo

Sample

Output 2

 1 #include<bits/stdc++.h>
 2 #define maxn 10005
 3 using namespace std;
 4 int n;
 5 int main()
 6 {
 7     scanf("%d",&n);
 8     getchar();
 9     for(int ii=1;ii<=n;ii++)
10     {
11         char a[100];
12         getchar();
13         scanf("%s",a);
14         int len=strlen(a);
15         int flag=0;
16         for(int i=1;i<=len;i++)
17         {
18             flag=0;
19             if((len%i)==0)
20              {for(int j=i;j<len;j++)
21                 if(a[j]!=a[j%i])
22                 {
23                    flag=1;break;
24                 }
25              }
26             else flag=1;
27             if(!flag)
28             {printf("%d",i);
29              break;}
30         }
31         if(ii==n)printf("\n");
32             else
33                 printf("\n\n");
34     }
35     return 0;
36 }

思路：

周期可能是[1,len]从小到大遍历所有可能，当可能是正确的，跳出循环。

如果字符串的长度是周期的倍数，该周期可能成立，否则一定是错的。

在上述成立的条件下，如果字符串的每一位，a[j]==a[j%i];则该周期成立。

注意点：

一开始没判断if((len%i)==0)。所以比如遇到这样的情况我一开始的代码会wa:abcabca