【HDU】1796 How many integers can you find

题意：给出n和m个元素的集合，求小于n且是集合中任意元素的倍数的数有多少个(m<=10)。

最基础的容斥了，懒得DFS，直接枚举二进制暴力完事。

 1 #include<cstdio>

 2 #include<algorithm>

 3 typedef long long LL;

 4 #define MAXN 110

 5 using namespace std;

 6 int n, m, ans;

 7 int a[MAXN];

 8 LL GCD(LL x, LL y) {

 9     return y ? GCD(y, x % y) : x;

10 }

11 LL LCM(LL x, LL y) {

12     return x / GCD(x, y) * y;

13 }

14 LL Get(int x, int &cnt) {

15     int i;

16     LL res = 1;

17     for (i = cnt = 0; i < m; i++) {

18         if (x & (1 << i)) {

19             cnt++;

20             res = LCM(res, a[i]);

21         }

22     }

23     return res;

24 }

25 int main() {

26     int i, k;

27     LL tmp;

28     while (~scanf("%d%d", &n, &m)) {

29         n--;

30         k = m;

31         for (ans = i = 0; i < m; i++) {

32             scanf("%d", &a[i]);

33             if (a[i] == 0)

34                 k = i;

35         }

36         if (k != m) {

37             m--;

38             swap(a[m], a[k]);

39         }

40         for (i = 1; i < (1 << m); i++) {

41             tmp = Get(i, k);

42             if (k & 1)

43                 ans += n / tmp;

44             else

45                 ans -= n / tmp;

46         }

47         printf("%d\n", ans);

48     }

49     return 0;

50 }