CF1152C
http://codeforces.com/contest/1152/problem/C

大意：给两个数a，b。让你找一个k，使得a+k与b+k的最小公倍数尽可能小，输出k
思路： gcd(a,b) = gcd(b,a-b)，最终得到的A，B，他们的gcd一定是a-b的因子

#include <bits/stdc++.h>
using namespace std;

// gcd(a,b) = gcd(b,a-b); -> (a-b)%gcd(a,b)==0
long long a,b,diff;
vector<long long> v;
int main(){
    cin>>a>>b;
    if(a>b)swap(a,b);
    diff = b-a;

    if(diff==0){
        cout<<0<<endl;
        goto _end;
    }
    long long ac,temp;
    ac=0,temp=diff+7;
    for(long long i=1;i*i<=diff;++i){ //枚举因子
        if(diff%i==0){
           v.push_back(i);
           v.push_back(diff/i);
        }
    }
    sort(v.begin(),v.end());
    int pos;
    pos = lower_bound(v.begin(),v.end(),a)-v.begin();
    if(pos<v.size()){
        ac = v[pos];
    }else
    while(ac<a){
        ac += diff; //如果上面没找见>=a的因子，那么找diff的倍数直到>=a
    }
    cout<<ac-a<<endl;

_end:
    return 0;
}