ZOJ - 3593 One Person Game （扩展欧几里得 技巧）

类似题目：

#include<iostream>
#include<cmath>
#define ll long long
#define INF 0x7fffffff
using namespace std;
ll exgcd(ll a,ll b,ll &x,ll &y)
{
    if(!b)
    {
        x=1;
        y=0;
        return a;
    }
    ll gcd=exgcd(b,a%b,x,y),t;
    t=x;
    x=y;
    y=t-a/b*y;
    return gcd;
}
int main()
{
    int t;
    cin>>t;
    while(t--)
    {
        ll A,B,a,b;
        ll x,y;
        cin>>A>>B>>a>>b;
        ll C=B-A;
        ll gcd=exgcd(a,b,x,y);
        if(C%gcd==0)
        {
            x*=C/gcd;
            y*=C/gcd;//通解形式
            ll mid=(y-x)*gcd/(a+b);
            ll minn=-1,ans=(ll)(INF)*(ll)(INF);
            for(ll i=mid-1;i<=mid+1;++i)
            {
                if((x+b/gcd*i)*(y-a/gcd*i)>=0)
                {
                    minn=max(fabs(x+b/gcd*i),fabs(y-a/gcd*i));
                }
                else
                {
                    minn=fabs(x+b/gcd*i)+fabs(y-a/gcd*i);
                }
                ans=min(ans,minn);

            }
            cout<<ans<<endl;

        }
        else cout<<"-1"<<endl;

    }
    return 0;
}