zoj 2836 容斥原理

题目链接：http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemCode=2836

#include <cstdio>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <cstring>
#include <queue>
#include <vector>

#define maxn 15
#define INF  0x3f3f3f
using namespace std;

int a[maxn];
int N;
long long ans,M;
int gcd(int a,int b){  //printf("%d %d\n",a,b);
    if(a%b == 0)  return b;
    else          return gcd(b,a%b);
}
int lcm(int a,int b){
    if(a<b){
        int temp = a;
        a = b;
        b = temp;
    }  
    return a*b/gcd(a,b);
}
void dfs(int u,int deep,int sum){
    for(int i=u+1;i<=N;i++){ 
        int temp = lcm(sum,a[i]);
        if(temp > M) return;
        if(deep%2) ans += M/temp; 
        else       ans -= M/temp;  
        dfs(i,deep+1,temp);
    }
}

int main()
{
    //freopen("input.txt","r",stdin);
    while(cin>>N>>M){
        for(int i=1;i<=N;i++)  cin>>a[i];
        sort(a+1,a+N+1);
        ans = 0;    
        dfs(0,1,1);    
        printf("%lld\n",ans);
    }
}