/**
* @brief Codeforces Round #275 (Div. 2) b
* @file b.cpp
* @author 面码
* @created 2014/12/11 18:09
* @edited 2014/12/11 18:09
* @type math binary search
*
*
*/
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <stack>
#include <string>
#include <set>
#include <cstring>
#include <cmath>
#include <vector>
using namespace std;
#define max(a, b) ((a) > (b) ? (a) : (b))
#define min(a, b) ((a) > (b) ? (b) : (a))
#define abs(a) ((a) > 0 ? (a) : (0 - (a)))
#define CLR(vec) memset(vec, 0, sizeof(vec))
#ifdef DEBUG
ifstream in;
ofstream out;
#define CIN in
#define COUT out
#else
#define CIN cin
#define COUT cout
#endif
#define MAXN (2e9 + 10)
typedef long long int ll;
ll lft, rht, mid;
ll cnt1, cnt2, x, y, z;
ll i, j, k;
ll need1, need2;
int main(void){
ios_base::sync_with_stdio(0);
#ifdef DEBUG
CIN.open("./in", ios::in);
COUT.open("./out", ios::out);
#endif
CIN >> cnt1 >> cnt2 >> x >> y;
z = x*y;
lft = 2; rht = MAXN;
while(lft < rht){
mid = ((rht - lft)/2 + lft);
/*set problem*/
i = mid - mid/x;
j = mid - mid/y;
k = mid - mid/z;
k = i + j - k;
i -= k;
j -= k;
#ifdef DEBUG
COUT << i << " " << j << " " << k << "\n";
#endif
if(i < cnt1)
k = k - (cnt1 - i);
if(j < cnt2)
k = k - (cnt2 - j);
if(k < 0)
lft = mid + 1; /*need more element*/
else
rht = mid; /*may get an answer more better*/
}
COUT << lft << endl;
return 0;
}
Codeforces Round #275 (Div. 2) b
原文：http://my.oschina.net/u/572632/blog/355252