中等递推题：
ans[i] = ans[i - 2] + ans[i - 1] + ( sum[i - 2] + cnt[i - 2] * len[i - 1] ) * cnt[i - 1] - sum[i - 1] * cnt[i - 2];
其中，ans[i]代表答案，cnt[i]代表ith个message中有多少个cff，sum[i]代表ith个message中cff的c的位置的和（从右向左index依次为1,2...），len[i]代表ith个message的长度。
1 #include <iostream> 2 #include <cstring> 3 #include <cstdio> 4 using namespace std; 5 6 typedef long long ll; 7 const int MOD = 530600414; 8 const int N = 201315; 9 int len[N]; 10 int sum[N]; 11 int ans[N]; 12 int cnt[N]; 13 14 void init() 15 { 16 len[1] = 1; 17 len[2] = 2; 18 len[3] = 3; 19 cnt[1] = cnt[2] = 0; 20 cnt[3] = 1; 21 sum[1] = sum[2] = 0; 22 sum[3] = 3; 23 ans[1] = ans[2] = ans[3] = 0; 24 for ( int i = 4; i < N; i++ ) 25 { 26 len[i] = ( len[i - 2] + len[i - 1] ) % MOD; 27 cnt[i] = ( cnt[i - 2] + cnt[i - 1] ) % MOD; 28 sum[i] = ( ( sum[i - 2] + ( ( ll ) cnt[i - 2] * len[i - 1] ) % MOD ) % MOD + sum[i - 1] ) % MOD; 29 int tmp1 = ( ans[i - 2] + ans[i - 1] ) % MOD; 30 int tmp2 = ( ( ( ll ) ( ( sum[i - 2] + ( ( ll ) cnt[i - 2] * len[i - 1] ) % MOD ) % MOD ) * cnt[i - 1] ) % MOD - ( ( ll ) sum[i - 1] * cnt[i - 2] ) % MOD + MOD ) % MOD; 31 ans[i] = ( tmp1 + tmp2 ) % MOD; 32 } 33 } 34 35 int main () 36 { 37 init(); 38 int t; 39 scanf("%d", &t); 40 for ( int _case = 1; _case <= t; _case++ ) 41 { 42 int n; 43 scanf("%d", &n); 44 printf("Case #%d: %d ", _case, ans[n]); 45 } 46 return 0; 47 }