【POI每日题解 #3】 OKR-Periods of Words

 1 #include <cstdio>
 2 #include <algorithm>
 3 using namespace std;
 4 const int N = 1e6 + 5;
 5 int len; 
 6 char str[N];
 7 int next[N];
 8 int main(){
 9     scanf("%d%s", &len, str);
10     int k = 0;
11     for(int i = 1; i < len; i++){
12         while(k > 0 && str[k] != str[i]) k = next[k];
13         if(str[k] == str[i]) k++;
14         next[i + 1] = k;
15     }
16     long long ans = 0;
17     for(int i = 1; i <= len; i++){
18         if(next[next[i]]) next[i] = next[next[i]]; 
19         ans += (long long)(i - (next[i] ? next[i] : i));
20     }
21     printf("%lld", ans);
22     return 0;    
23 }