Codeforces 724C Ray Tracing 扩展欧几里得

#include<iostream>
#include<cstring>
#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<iomanip>
#include<map>
#include<set>
#include<vector>
#include<ctime>
#include<cmath>
#define LL long long
using namespace std;
#define LL long long
#define up(i,j,n) for(int i=(j);(i)<=(n);(i)++)
#define max(x,y) ((x)<(y)?(y):(x))
#define min(x,y) ((x)<(y)?(x):(y))
#define FILE "1"
const int maxn=101000;
const LL inf=10000000000000LL;
int n,m,k;
void init(){
scanf("%d%d%d",&n,&m,&k);
}
void gcd(LL a,LL b,LL &d,LL &x,LL &y){
if(b==0){d=a;x=1;y=0;return;}
gcd(b,a%b,d,x,y);
int t=x;
x=y;
y=t-a/b*x;
return;
}
LL t(LL a,LL b,LL c,LL &x,LL &y ){
LL d;gcd(a,b,d,x,y);
if(c%d)return -1;
LL ran=b/d;if(ran<0)ran=-ran;
x*=c/d;
x=(x%ran+ran)%ran;
return 0;
}
LL get(LL x,LL y,LL maxx){
LL K,S;
if(t(2*n,-2*m,y-x,K,S)==-1)return maxx+1;
LL ans=2*K*n+x;
if(ans<0||ans>maxx)return maxx+1;
return ans;
}
LL gcd(LL a,LL b){return b?gcd(b,a%b):a;}
LL work(LL x,LL y){
LL maxx=1LL*n/gcd(n,m)*m;
LL minn=maxx+1;
minn=min(get(x,y,maxx),minn);
minn=min(get(-x,y,maxx),minn);
minn=min(get(x,-y,maxx),minn);
minn=min(get(-x,-y,maxx),minn);
if(minn==maxx+1)return -1;
else return minn;
}
void slove(){
init();
up(i,1,k){
LL x,y;
scanf("%I64d%I64d",&x,&y);
printf("%I64d\n",work(x,y));
}
}
int main(){
slove();
}