HDU 2048 神、上帝以及老天爷

错排公式

 1 #include <algorithm>
 2 #include <iostream>
 3 #include <cstring>
 4 #include <cstdio>
 5 #include <cctype>
 6 
 7 using namespace std;
 8 
 9 inline void read(long long &x)
10 {
11     int k = 1; x = 0;
12     char c = getchar();
13     while (!isdigit(c))
14         if (c == '-') k = - 1, c = getchar();
15         else c = getchar();
16     while (isdigit(c))
17         x = (x << 1) + (x << 3) + (c ^ 48),
18         c = getchar();
19     x *= k;
20 }
21 
22 long long T, n, dp[55], mul[55];
23 
24 int main()
25 {
26     read(T), mul[0] = 1;
27     for (int i = 1; i <= 30; ++i) 
28         mul[i] = mul[i - 1] * i;
29     for (int plk = 1; plk <= T; ++plk)
30     {
31         read(n);
32         memset(dp, 0, sizeof(dp));
33         dp[0] = 0, dp[1] = 0, dp[2] = 1;
34         for (int i = 3; i <= n; ++i)
35             dp[i] = (i - 1) * (dp[i - 1] + dp[i - 2]); 
36         printf("%.2lf%%\n", 100 * (double)dp[n] / (double)mul[n]);
37     }
38     return 0;
39 }

 

posted @ 2018-12-13 10:10  Christopher_Yan  阅读(171)  评论(0)  编辑  收藏  举报