hdu 1796 容斥原理（dfs）

很基本的容斥原理的题目，注意要先把0去掉。
 1 #include <iostream>
 2 #include <cstring>
 3 #include <cstdio>
 4 using namespace std;
 5 
 6 typedef long long ll;
 7 const int N = 10;
 8 int s[N];
 9 bool visit[N];
10 int n, m, ans;
11 
12 ll gcd( ll x, ll y )
13 {
14     return y ? gcd( y, x % y ) : x;
15 }
16 
17 ll lcm( ll x, ll y )
18 {
19     return x / gcd( x, y ) * y;
20 }
21 
22 void dfs( int cur )
23 {
24     if ( cur == m )
25     {
26         int cnt = 0, r = 1;
27         ll d = 1;
28         for ( int i = 0; i < m; i++ )
29         {
30             if ( visit[i] )
31             {
32                 d = lcm( d, s[i] );
33                 cnt++;
34             }
35         }
36         if ( cnt == 0 ) return ;
37         if ( cnt % 2 == 0 ) r = -1;            
38         ans += n / d * r;
39         return ;
40     }    
41     visit[cur] = 0;
42     dfs( cur + 1 );
43     visit[cur] = 1;
44     dfs( cur + 1 );
45     return ;
46 }
47 
48 int main ()
49 {
50     while ( scanf("%d%d", &n, &m) != EOF )
51     {
52         int tn = 0;
53         for ( int i = 0; i < m; i++ )
54         {
55             int tmp;
56             scanf("%d", &tmp);
57             if ( tmp != 0 )
58             {
59                 s[tn++] = tmp;
60             }
61         }
62         m = tn;
63         ans = 0;
64         n--;
65         dfs(0);
66         printf("%d
", ans);
67     }
68     return 0;
69 }