题目链接:http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemId=3754
There is a very simple and interesting one-person game. You have 3 dice, namely Die1, Die2 and Die3. Die1 has K1 faces. Die2 has K2 faces. Die3 has K3 faces. All the dice are fair dice, so the probability of rolling each value, 1 to K1, K2, K3 is exactly 1 / K1, 1 / K2 and 1 / K3. You have a counter, and the game is played as follow:
Calculate the expectation of the number of times that you cast dice before the end of the game.
Input
There are multiple test cases. The first line of input is an integer T (0 < T <= 300) indicating the number of test cases. Then T test cases follow. Each test case is a line contains 7 non-negative integers n, K1, K2, K3, a, b, c (0 <= n <= 500, 1 < K1, K2, K3 <= 6, 1 <= a <= K1, 1 <= b <= K2, 1 <= c <= K3).
Output
For each test case, output the answer in a single line. A relative error of 1e-8 will be accepted.
Sample Input
2 0 2 2 2 1 1 1 0 6 6 6 1 1 1
Sample Output
1.142857142857143 1.004651162790698
PS:http://blog.csdn.net/morgan_xww/article/details/6775853
代码如下:
#include <cstdio> #include <cstring> int main() { int t; int n; int k1, k2 ,k3; int a, b, c; double p[47]; scanf("%d",&t); while(t--) { memset(p,0,sizeof(p)); scanf("%d%d%d%d%d%d%d",&n,&k1,&k2,&k3,&a,&b,&c); double p0 = 1.0/(k1*k2*k3); for(int i = 1; i <= k1; i++) { for(int j = 1; j <= k2; j++) { for(int k = 1; k <= k3; k++) { if(i!=a || j!=b || k!=c) { p[i+j+k] += p0; } } } } double a[700], b[700]; memset(a, 0,sizeof(a)); memset(b, 0,sizeof(b)); for(int i = n; i >= 0; i--) { for(int k = 3; k <= k1+k2+k3; k++) { a[i] += a[i+k] * p[k]; b[i] += b[i+k] * p[k]; } a[i]+=p0; b[i]+=1; } printf("%.15lf\n",b[0]/(1-a[0])); } return 0; }