Luogu 3435 POI2006OKR-Periods of Words（kmp）

　　显然答案应该是Σi-next[next[……next[i]]] (next[next[……next[i]]]>0)。递推即可。

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<algorithm>
using namespace std;
int read()
{
    int x=,f=;char c=getchar();
    while (c<''||c>'') {if (c=='-') f=-;c=getchar();}
    while (c>=''&&c<='') x=(x<<)+(x<<)+(c^),c=getchar();
    return x*f;
}
#define N 1000010
int n,nxt[N],f[N];
long long ans=;
char s[N];
int main()
{
#ifndef ONLINE_JUDGE
    freopen("a.in","r",stdin);
    freopen("a.out","w",stdout);
    const char LL[]="%I64d\n";
#else
    const char LL[]="%lld\n";
#endif
    n=read();scanf("%s",s+);
    nxt[]=-;
    for (int i=;i<=n;i++)
    {
        int j=nxt[i-];
        while (~j&&s[j+]!=s[i]) j=nxt[j];
        nxt[i]=j+;f[i]=nxt[i]==?i:f[nxt[i]];
    }
    for (int i=;i<=n;i++) ans+=i-f[i];
    cout<<ans;
    return ;
}