答案就是n-fail[n](n-next[n])，至于为什么，自己画个图看看就好了。
1 #include<bits/stdc++.h> 2 #define N 1000005 3 #define LL long long 4 #define inf 0x3f3f3f3f 5 using namespace std; 6 inline int ra() 7 { 8 int x=0,f=1; char ch=getchar(); 9 while (ch<'0' || ch>'9') {if (ch=='-') f=-1; ch=getchar();} 10 while (ch>='0' && ch<='9') {x=x*10+ch-'0'; ch=getchar();} 11 return x*f; 12 } 13 char ch[N]; 14 int fail[N]; 15 int main() 16 { 17 int L=ra(); scanf("%s",ch+1); 18 int fix=0; 19 for (int i=2; i<=L; i++) 20 { 21 while (ch[fix+1]!=ch[i] && fix) fix=fail[fix]; 22 if (ch[fix+1]==ch[i]) fix++; 23 fail[i]=fix; 24 } 25 printf("%d",L-fail[L]); 26 return 0; 27 }