codeforces B. Friends and Presents(二分+容斥)

 1 #include<iostream> 
 2 #include<cstring>
 3 #include<cstdio>
 4 #include<algorithm>
 5 using namespace std;
 6 
 7 int gcd(int x, int y){
 8     return y==0 ? x : gcd(y, x%y);
 9 }
10 
11 int lcm(int x, int y){
12     return x*y/gcd(x, y);
13 }
14 
15 int main(){
16     long long ld = 1, rd = 100000000000000ll, mid;
17     long long c1, c2, x, y;
18     cin>>c1>>c2>>x>>y;
19     while(ld <= rd){
20         mid = (ld + rd)>>1;
21         long long s1 = mid/x, s2 = mid/y, s3 = mid/lcm(x, y);
22         if(mid-s1 >= c1 && mid-s2 >= c2 && mid-s3 >= c1+c2) rd = mid-1;
23         else ld = mid+1;
24     }    
25     cout<<rd+1<<endl;
26     return 0;
27 }