luogu2455 [SDOI2006]线性方程组 高斯消元法

#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
int n, x;
double a[55][55];
const double eps=1e-7;
void gauss(){
	for(int i=1; i<=n; i++){
		int maxi=i;
		for(int j=i+1; j<=n; j++)
			if(a[j][i]>a[maxi][i])
				maxi = j;
		swap(a[maxi], a[i]);
		double now=a[i][i];
		if(fabs(now)<eps)	continue;
		for(int j=i; j<=n+1; j++)
			a[i][j] /= now;
		for(int j=1; j<=n; j++)
			if(i!=j){
				now = a[j][i];
				for(int k=i; k<=n+1; k++)
					a[j][k] -= now * a[i][k];
			}
	}
	bool wj=false, oo=false;
	for(int i=1; i<=n; i++){
		int j=1;
		while(j<=n+1 && fabs(a[i][j])<eps)	j++;
		if(j==n+1)	wj = true;//倘若是0..0..0....x则无解
		if(j>n+1)	oo = true;//倘若是0..0..0....0则无穷解
	}
	if(wj)	printf("-1\n");//只要敢有无解的整个方程就无解
	else if(oo)	printf("0\n");
	else
		for(int i=1; i<=n; i++)
			if(fabs(a[i][n+1])<eps)	printf("x%d=0\n", i);
			else	printf("x%d=%.2lf\n", i, a[i][n+1]);
}
int main(){
	cin>>n;
	for(int i=1; i<=n; i++)
		for(int j=1; j<=n+1; j++){
			scanf("%d", &x);
			a[i][j] = x;
		}
	gauss();
	return 0;
}