hdu 3336（KMP算法的应用）

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=3336

Count the string

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 4844    Accepted Submission(s): 2294

Problem Description

It is well known that AekdyCoin is good at string problems as well as number theory problems. When given a string s, we can write down all the non-empty prefixes of this string. For example:
s: "abab"
The prefixes are: "a", "ab", "aba", "abab"
For each prefix, we can count the times it matches in s. So we can see that prefix "a" matches twice, "ab" matches twice too, "aba" matches once, and "abab" matches once. Now you are asked to calculate the sum of the match times for all the prefixes. For "abab", it is 2 + 2 + 1 + 1 = 6.
The answer may be very large, so output the answer mod 10007.

 

Input

The first line is a single integer T, indicating the number of test cases.
For each case, the first line is an integer n (1 <= n <= 200000), which is the length of string s. A line follows giving the string s. The characters in the strings are all lower-case letters.

 

Output

For each case, output only one number: the sum of the match times for all the prefixes of s mod 10007.

 

Sample Input

14abab

 

Sample Output

6

 

思路：要想解出这道题就得先理解next[]的求法和含义；

#include <iostream>#include <string.h>#include <string>#include <stdio.h>const int N=200000+100;const int mod=10007;using namespace std;int n,next[N];char s[N];void get_next() //求出next[]{  int i=1,j=0;  while(i<=n)  {    if(j==0||s[i]==s[j])    {      ++i;      ++j;      next[i]=j;    }    else      j=next[j];  }}int main(){     int T;     cin>>T;     while(T--)     {      scanf("%d",&n);      scanf("%s",s+1);      get_next();      int cnt=0;      cnt=(cnt+n)%mod;      for(int i=3;i<=n+1;i++)      {        if(next[i]>=2)        {          cnt=(cnt+1)%mod;        }      }      printf("%d\n",cnt);     }     return 0;}