ZOJ2836 Number Puzzle
? 解题记录 ? ? 杂OJ ? ? 容斥 ?    2018-08-21 11:01:23    575    0    0

Given a list of integers (A1, A2, ..., An), and a positive integer M, please find the number of positive integers that are not greater than M and dividable by any integer from the given list.

Input

The input contains several test cases.

For each test case, there are two lines. The first line contains N (1 <= N <= 10) and M (1 <= M <= 200000000), and the second line contains A1, A2, ..., An(1 <= Ai <= 10, for i = 1, 2, ..., N).

Output

For each test case in the input, output the result in a single line.

Sample Input

3 2
2 3 7
3 6
2 3 7

Sample Output

1
4

## 简单容斥，枚举集合，大小奇数加、偶数减就行了。计算至少能被一些数整除的个数直接用M/LCM就行了。

```#include<cstdio>
#include<cstring>
#include<cmath>
#define LL long long
using namespace std;
int a[15], n, m;
LL ans;
LL gcd(LL a, LL b) {
return b ? gcd(b, a % b) : a;
}
void GetAns(int step, LL cnt, int rw) {
if(cnt > m) return;
if(step == n + 1) {
ans += (m / cnt) * rw;
return ;
}
GetAns(step + 1, cnt * a[step] / gcd(a[step], cnt), rw * (-1));
GetAns(step + 1, cnt, rw);
}

int main() {
while(~scanf("%d%d", &n, &m)) {
ans = 0;
for(register int i = 1; i <= n; ++i)
scanf("%d", &a[i]);
GetAns(1, 1, 1);
printf("%d\n", m - ans);
}
return 0;
}```

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