HDU 3579 线性同余方程组

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

const int MaxM=11;

int a[MaxM],b[MaxM];

void exgcd(int a,int b,int &d,int &x,int &y){
	if(b==0){
		x=1; y=0;
		d=a;
	}
	else{
		exgcd(b,a%b,d,x,y);
		int tmp=x;
		x=y;
		y=tmp-(a/b)*y;
	}
}

int gcd(int a,int b){
	if(b==0) return a;
	return gcd(b,a%b);
}

int main(){
	int t; int a1,r1,a2,r2; int aa,bb,cc,dd; int x,y; int g;
	scanf("%d",&t);
	int n,m;
	bool ifhave;
	int kase=0;
	while(t--){
		kase++;
		scanf("%d",&m);
		g=1;
		for(int i=0;i<m;i++){
			scanf("%d",&a[i]);
			if(i==0){ g=a[i]; continue; }
			g=g*a[i]/gcd(g,a[i]);
		}
		for(int i=0;i<m;i++)
		scanf("%d",&b[i]);
		a1=a[0]; r1=b[0];
		ifhave=true;
		for(int i=1;i<m;i++){
			a2=a[i]; r2=b[i];
			aa=a1; bb=a2; cc=r2-r1;
			exgcd(aa,bb,dd,x,y);
			if(cc%dd!=0){
				ifhave=false;
				break;
			}
			int t=bb/dd;
			x=(x*(cc/dd)%t+t)%t;
			r1=a1*x+r1;
			a1=a1*(a2/dd);
		}
		printf("Case %d: ",kase);
		if(!ifhave)
		printf("-1\n");
		else{
			if(r1==0)
			printf("%d\n",g);
			else printf("%d\n",r1);
		}
	}
	return 0;
}