Codeforces 535D Tavas and Malekas KMP

 1 // File Name: d.cpp
 2 // Author: darkdream
 3 // Created Time: 2015年04月15日 星期三 14时45分20秒
 4 
 5 #include<vector>
 6 #include<list>
 7 #include<map>
 8 #include<set>
 9 #include<deque>
10 #include<stack>
11 #include<bitset>
12 #include<algorithm>
13 #include<functional>
14 #include<numeric>
15 #include<utility>
16 #include<sstream>
17 #include<iostream>
18 #include<iomanip>
19 #include<cstdio>
20 #include<cmath>
21 #include<cstdlib>
22 #include<cstring>
23 #include<ctime>
24 #define LL long long
25 #define M 1000000007
26 using namespace std;
27 char str[1000005];
28 int a[1000005];
29 int next[1000005];
30 int hs[1000005];
31 int len ; 
32 void get_next()
33 {
34     int  k = -1;
35      next[0] = -1;
36     int j = 0 ; 
37     while(j < len){
38         if(k == -1 || str[j] == str[k]){
39             ++ k ; 
40             ++ j ;
41             next[j] = k ; 
42         }else{
43             k = next[k];
44         }
45     }
46 }
47 void dfs(int k){
48    if(k == 0 )
49        return ;
50    hs[len - k + 1] = 1; 
51    dfs(next[k]);
52 }
53 LL Pow(int k)
54 {
55     if(k < 0)
56         return 0;
57     LL ans = 1;
58     for(int i = 1;i <= k; i ++)
59         ans = ans * 26 % M; 
60     return ans;
61 }
62 int main(){
63     int n , m ; 
64     scanf("%d %d",&n,&m);
65     scanf("%s",str);
66     len = strlen(str);
67     get_next();
68     dfs(next[len]);
69     LL ans = 1 ; 
70     if(m != 0 )
71     {
72     scanf("%d",&a[1]);
73     ans = Pow(a[1]-1);
74     }
75     for(int i= 2;i<= m;i++){
76         scanf("%d",&a[i]);
77         if(a[i] - a[i-1] < len)
78         {
79             if(hs[a[i]-a[i-1]+1] == 0 )
80             {
81                 printf("0\n");
82                 return 0 ; 
83             }
84         }else{
85           ans = ans * Pow(a[i]-a[i-1]-len)%M;
86         }
87     }
88     //printf("%d %I64d\n",n-a[m]-len+1,ans);
89     if(m != 0 )
90     ans  = ans * Pow(n-a[m]-len + 1) % M;
91     else 
92         ans = Pow(n);
93   //  for(int i= 1;i <= len ;i ++)
94     //    printf("%d ",hs[i]);
95     printf("%I64d\n",ans);
96 return 0;
97 }