HDU 1796 How many integers can you find（容斥原理）

http://acm.hdu.edu.cn/showproblem.php?pid=1796

这篇文章对容斥原理讲解很清楚 http://www.cppblog.com/vici/archive/2011/09/05/155103.html

View Code

 1 #include <iostream>

 2 #include<cstdio>

 3 #include<string.h>

 4 #include<cmath>

 5 #define LL long long

 6 using namespace std;

 7 LL sum,x[21],n;

 8 int m;

 9 int gcd(int x,int y)

10 {

11     return y==0?x:gcd(y,x%y);

12 }

13 void dfs(int num,int i,LL y)

14 {

15     int j;

16     y = y*x[i]/(gcd(y,x[i]));

17     if(num%2!=0)

18     sum+=(n-1)/y;

19     else

20     sum-=(n-1)/y;

21     for(j = i+1 ; j <= m ; j++)

22     {

23         if(x[j]!=0)

24         dfs(num+1,j,y);

25     }

26 }

27 int main()

28 {

29     int i,j,k;

30     while(cin>>n>>m)

31     {

32         sum = 0;

33         for(i = 1; i <= m ; i++)

34         cin>>x[i];

35         for(i = 1 ; i <= m ; i++)

36         {

37             if(x[i]!=0)

38             dfs(1,i,x[i]);

39         }

40         cout<<sum<<endl;

41     }

42     return 0;

43 }