最后化简成
k1 * x1 = a
k2 * x2 = b
如果 k1 = 0 a != 0则无解
如果 k1 = 0 a = 0则无穷解

注意要先判断无解再判断无穷解QWQ

#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm>
#include<cstring>

using namespace std;

int n,nowline;
double a[11451][11451];

inline int find_pivot( int line , int column ) {
	//line:行 column:列 
	int maxn = line;
	for (int i = line + 1; i <= n; ++i) {
		if ( a[i][column] > a[maxn][column] ) {
			maxn = i;
		}
	}
	return maxn;
}

inline void swap_line( int now , int need ) {
	//now表示现在这一行 need表示需要的行
	for (int i = 1; i <= n + 1; ++i) {
		swap( a[now][i] , a[need][i] );
	} 
	return; 
}

int main()
{
	scanf("%d",&n);
	for (int i = 1; i <= n; ++i) {
		for (int j = 1; j <= n + 1; ++j) {
			scanf("%lf",&a[i][j]);
		}
	}
	for (int q = 1,i = 1; q <= n; ++q) {
		//i表示第几行 q表示第几列 
		int pivot = find_pivot( i , q );
		//这里一定要注意find时的行与列 QWQ 
		if ( a[pivot][q] == 0 ) continue;
		//如果此列全为0则先跳过,可以先不用管 
		swap_line( i , pivot ); 
		for (int j = 1; j <= n; ++j) {
			if ( j != i ) {
				double temp = a[j][q] / a[i][q];
				for (int k = q;k <= n + 1; ++k) {
					a[j][k] -= ( a[i][k] * temp );
				}
			}
		}//正常高斯约旦消元 
		i ++;
		nowline = i;
	}
	if ( nowline <= n ) {
		for (int i = nowline; i <= n; ++i) {
			if ( a[i][n + 1] != 0 ) {
				//其中有k * x = a;
				//若 k = 0 a != 0 则无解 输出-1 
				//若 k = 0 a = 0 则无穷解 输出0 
				//注意在同时是无解和无穷解的情况下方程组属于无解 
				printf ("-1\n");
				return 0;
			}
		}
		printf ("0\n");
		return 0;
	}
	for (int i = 1; i <= n; ++i) {		
		a[i][n + 1] /= a[i][i];//除上系数
		printf ( "x%d=" , i );
		if ( fabs( a[i][n + 1] ) == 0 ) a[i][n + 1] = 0;
		printf ( "%.2lf\n" , a[i][n + 1] );
	}
	return 0;
}