简介
贪心算法（又称贪婪算法）是指，在对问题求解时，总是做出在当前看来是最好的选择。也就是说，不从整体最优上加以考虑，他所做出的是在某种意义上的局部最优解。
贪心算法不是对所有问题都能得到整体最优解，关键是贪心策略的选择，选择的贪心策略必须具备无后效性，即某个状态以前的过程不会影响以后的状态，只与当前状态有关。
FatMouse’ Trade
FatMouse’ Trade
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 33703 Accepted Submission(s): 10981
Problem Description
FatMouse prepared M pounds of cat food, ready to trade with the cats guarding the warehouse containing his favorite food, JavaBean.
The warehouse has N rooms. The i-th room contains J[i] pounds of JavaBeans and requires F[i] pounds of cat food. FatMouse does not have to trade for all the JavaBeans in the room, instead, he may get J[i]* a% pounds of JavaBeans if he pays F[i]* a% pounds of cat food. Here a is a real number. Now he is assigning this homework to you: tell him the maximum amount of JavaBeans he can obtain.
Input
The input consists of multiple test cases. Each test case begins with a line containing two non-negative integers M and N. Then N lines follow, each contains two non-negative integers J[i] and F[i] respectively. The last test case is followed by two -1’s. All integers are not greater than 1000.
Output
For each test case, print in a single line a real number accurate up to 3 decimal places, which is the maximum amount of JavaBeans that FatMouse can obtain.
Sample Input
5 3
7 2
4 3
5 2
20 3
25 18
24 15
15 10
-1 -1
Sample Output
13.333
31.500
贪心思想
从每傍食物最便宜的开始
C++代码
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#include<iostream> #include<algorithm> using namespace std; struct bean{ double pound; double value; double perv; bool operator < (const bean &A)const{ return perv > A.perv; } }buff[100]; int main(){ int n; double m; while(cin>>m>>n){ if(m == -1 && n == -1)break; for(int i = 0; i < n; i++){ scanf("%lf%lf", &buff[i].pound, &buff[i].value); buff[i].perv = buff[i].pound/buff[i].value; } sort(buff, buff + n); int id = 0; double ans = 0; while(m > 0 && id < n){ if(m > buff[id].value){ m -= buff[id].value; ans += buff[id].pound; }else{ ans += m*buff[id].perv; m = 0; } id++; } cout<<ans<<endl; } return 0; } /* 5 3 7 2 4 3 5 2 20 3 25 18 24 15 15 10 -1 -1 */ |
今年暑假不AC
“今年暑假不AC？”
“是的。”
“那你干什么呢？”
“看世界杯呀，笨蛋！”
“@#$%^&*%…”
确实如此，世界杯来了，球迷的节日也来了，估计很多ACMer也会抛开电脑，奔向电视了。
作为球迷，一定想看尽量多的完整的比赛，当然，作为新时代的好青年，你一定还会看一些其它的节目，比如新闻联播（永远不要忘记关心国家大事）、非常6+7、超级女生，以及王小丫的《开心辞典》等等，假设你已经知道了所有你喜欢看的电视节目的转播时间表，你会合理安排吗？（目标是能看尽量多的完整节目）
Input
输入数据包含多个测试实例，每个测试实例的第一行只有一个整数n(n<=100)，表示你喜欢看的节目的总数，然后是n行数据，每行包括两个数据Ti_s,Ti_e (1<=i<=n)，分别表示第i个节目的开始和结束时间，为了简化问题，每个时间都用一个正整数表示。n=0表示输入结束，不做处理。
Output
对于每个测试实例，输出能完整看到的电视节目的个数，每个测试实例的输出占一行。Sample Input
12
1 3
3 4
0 7
3 8
15 19
15 20
10 15
8 18
6 12
5 10
4 14
2 9
0
贪心思想
按照结束时间的早晚来，先看结束时间早的
C++代码
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#include<iostream> #include<algorithm> using namespace std; struct prog{ int start; int endx; bool operator < (const prog &A)const{ return endx < A.endx; } }buff[10000]; int main(){ int n; while(cin>>n){ if(n == 0)break; int ans = 1, time = 0; for(int i = 0; i < n; i++){ cin>>buff[i].start>>buff[i].endx; } sort(buff, buff + n); time = buff[0].endx; for(int i = 1; i < n; i++){ if(buff[i].start >= time){ ans++; time = buff[i].endx; } } cout<<ans<<endl; } return 0; } |
