贪心算法

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。

具体代码如下所示：

#include <cstdio>#include <iostream>#include <ctime>#include <windows.h>#include <algorithm>#include <fstream>using namespace std;struct activity{ int no; int start; int finish;};bool cmp(const activity &x, const activity &y){ return x.finish<y.finish;//从小到大排<，若要从大到小排则>}int greedySelector(int m,int solution[],struct activity activity[]){ int number = 1; solution[0] = 1; int i,j = 0,counter = 1; for(i = 1;i < m ;i++) { if(activity[i].start >=activity[j].finish) { solution[i] = 1; j = i; counter++; } else solution[i] = 0; } cout << "The amount of activities is:"<<counter<<endl; cout << "The solution is:"; for(i = 0 ;i < m ;i++) { if (solution[i] == 1) { cout << activity[i].no <<" "; } } return counter;}int main(void){ LARGE_INTEGER nFreq; LARGE_INTEGER nBeginTime; LARGE_INTEGER nEndTime; ofstream fout; srand((unsigned int)time(NULL)); int m,i,j,t; double cost; cout << "Please enter the number of times you want to run the program:"; cin >> t; fout.open("activity.txt",ios::app); if(!fout){ cerr<<"Can not open file 'activity.txt' "<<endl; return -1; } fout.setf(ios_base::fixed,ios_base::floatfield); //防止输出的数字使用科学计数法 for (j = 0;j < t;j++) { cout << "——————————————————The "<< j + 1 << "th test —————————————————"<<endl; m = 1 + rand()%100000; fout<<m<<","; int solution[m]; activity activity[m]; for( i = 0;i < m;i++) { activity[i].no = i+1; activity[i].start = 1 + rand()%1000; while(1) { activity[i].finish = 1 + rand()%10000; if(activity[i].finish > activity[i].start) break; } } QueryPerformanceFrequency(&nFreq); QueryPerformanceCounter(&nBeginTime); sort(activity,activity+m,cmp); greedySelector(m,solution,activity); QueryPerformanceCounter(&nEndTime); cost=(double)(nEndTime.QuadPart - nBeginTime.QuadPart) / (double)nFreq.QuadPart; fout << cost << endl; cout << "\nThe running time is:" << cost << " s" << endl; } fout.close(); cout << endl << endl; cout << "Success!" << endl; return 0;}

总结

以上所述是小编给大家介绍的C++贪心算法实现活动安排问题，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对网站的支持！
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