Description
The aspiring Roy the Robber has seen a lot of American movies, and knows that the bad guys usually gets caught in the end, often because they become too greedy. He has decided to work in the lucrative business of bank robbery only for a short while, before retiring to a comfortable job at a university.
For a few months now, Roy has been assessing the security of various banks and the amount of cash they hold. He wants to make a calculated risk, and grab as much money as possible.
His mother, Ola, has decided upon a tolerable probability of getting caught. She feels that he is safe enough if the banks he robs together give a probability less than this.
For a few months now, Roy has been assessing the security of various banks and the amount of cash they hold. He wants to make a calculated risk, and grab as much money as possible.
His mother, Ola, has decided upon a tolerable probability of getting caught. She feels that he is safe enough if the banks he robs together give a probability less than this.
Input
The first line of input gives T, the number of cases. For each scenario, the first line of input gives a floating point number P, the probability Roy needs to be below, and an integer N, the number of banks he has plans for. Then follow N lines, where line j gives an integer Mj and a floating point number Pj .
Bank j contains Mj millions, and the probability of getting caught from robbing it is Pj .
Bank j contains Mj millions, and the probability of getting caught from robbing it is Pj .
Output
For each test case, output a line with the maximum number of millions he can expect to get while the probability of getting caught is less than the limit set.
Notes and Constraints
0 < T <= 100
0.0 <= P <= 1.0
0 < N <= 100
0 < Mj <= 100
0.0 <= Pj <= 1.0
A bank goes bankrupt if it is robbed, and you may assume that all probabilities are independent as the police have very low funds.
Notes and Constraints
0 < T <= 100
0.0 <= P <= 1.0
0 < N <= 100
0 < Mj <= 100
0.0 <= Pj <= 1.0
A bank goes bankrupt if it is robbed, and you may assume that all probabilities are independent as the police have very low funds.
Sample Input 3 0.04 3 1 0.02 2 0.03 3 0.05 0.06 3 2 0.03 2 0.03 3 0.05 0.10 3 1 0.03 2 0.02 3 0.05 Sample Output 2 4 6
题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=2955
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题意：Roy想要抢劫银行，每家银行多有一定的金额和被抓到的概率，知道Roy被抓的最大概率P，求Roy在不被抓的情况下，抢劫最多。
分析：
当前的概率基于前一种状态的概率，即偷n家银行而不被抓的概率等于偷n-1家银行不被转的概率乘以偷第n家银行不被抓的概率。
用dp[i]表示偷价值为 i 时不被抓的概率，则状态转移方程为：
dp[j] = max(dp[j] , dp[j-m[i]] * (1-p[i]));
原意是提供银行个数和期望被捕概率，然后将每个银行的钱数和逃脱概率给出，通过将总数当作背包大小，通过求最大逃脱概率当作最大价值（但是并不是求这个），最终通过从总钱数递减找到低于期望被捕概率第一项背包， 即为不被逮捕的所能强盗的最大钱数。
AC代码：
1 #include<iostream> 2 #include<algorithm> 3 #include<cstdio> 4 #include<cstring> 5 #include<queue> 6 #include<stdlib.h> 7 #include<map> 8 #include<cmath> 9 10 using namespace std; 11 12 #define N 25000 13 #define INF 0x3f3f3f3f 14 15 double dp[N]; 16 17 int main() 18 { 19 int T,n,m[N],i,j,sum; 20 double p,g[250]; 21 22 scanf("%d", &T); 23 24 while(T--) 25 { 26 scanf("%lf %d", &p,&n); 27 28 sum=0; 29 p=1-p;///安全逃脱的概率 30 31 for(i=0;i<n;i++) 32 { 33 scanf("%d %lf",&m[i], &g[i]); 34 sum+=m[i];///抢劫所有的银行的金额 35 g[i]=1-g[i];///抢劫每家银行的逃脱概率 36 } 37 38 memset(dp,0,sizeof(dp)); 39 dp[0]=1; 40 41 for(i=0;i<n;i++) 42 for(j=sum;j>=m[i];j--) 43 if(dp[j]<dp[j-m[i]]*g[i]) 44 dp[j]=dp[j-m[i]]*g[i];///小偷偷j钱逃脱的最大概率 45 46 for(i=sum;i>=0;i--)///安全逃脱概率下偷盗最多的钱 47 if(dp[i]>=p) 48 { 49 printf("%d\n", i); 50 break; 51 } 52 53 /*for(i=sum;i>=0&&dp[i]<p;i--); 54 printf("%d\n", i);/*/ 55 56 } 57 return 0; 58 }
/假设你有一个数组int a[5];那么你可以这样给数组赋值
for(int i = 0;i<5;i++)
a[i]=i;
这个是没加分号的，那么a[0]=0,a[1]=1....a[4]=4;
for(int i = 0;i<5;i++);这样加了分号，就代表结束了，相当于循环只执行了i，然后就退出循环了
a[i]=i;//这样相当于只有a[4]=4;
