大概是0的情况也输出-1了，求hack

#include<bits/stdc++.h>
using namespace std;
const double eps=1e-7;
const int maxn=1e3+10;
double a[maxn][maxn],ans[maxn],bj[maxn],lt,op=0;
int n;
int main(){
	cin>>n;
	for(int i=1;i<=n;i++)for(int j=1;j<=n+1;j++)cin>>a[i][j];
	if(n==1&&a[1][1]==0&&a[1][2]){cout<<-1;return 0;}
	for(int i=1;i<=n;i++){
		int r=i;
		for(int j=i+1;j<=n;j++)if(fabs(a[j][i])>fabs(a[r][i]))r=j;
		if(fabs(a[r][i])<eps){op=999;continue;}
		double d=a[r][i];
		if(i!=r)swap(a[i],a[r]);
		for(int j=i;j<=n+1;j++){a[i][j]/=d;}
		for(int j=i+1;j<=n;j++){
			d=a[j][i];
			for(int k=i;k<=n+1;k++)a[j][k]-=a[i][k]*d;
		}
	}
	
//	for(int i=1;i<=n;i++){
//		for(int j=1;j<=n;j++)cout<<a[i][j]<<" ";
//		cout<<"\n";
//	}
	ans[n]=a[n][n+1];
	int sum=n-1;
	while(sum>=1){
			for(int i=n-1;i>=1;i--){
				if(a[i][sum]){bj[i]=1;
					ans[sum]=a[i][n+1];
					for(int j=sum+1;j<=n;j++)ans[sum]-=a[i][j]*ans[j];
					break;
				}
			}
			sum--;
	}
	for(int i=1;i<=n-1;i++)if(bj[i]==0){cout<<-1;return 0;}
	if(op==999){cout<<0;return 0;}
	for(int i=1;i<=n;i++)printf("x%d=%.2lf\n",i,ans[i]);	
	return 0;
}
//4
//0 0 2 1 2
//0 0 1 1 1
//0 0 0 1 1
//0 0 0 0 0