90 pts 求助 WA on #9 #12 #13（悬三关）

rt。

#include<bits/stdc++.h>
using namespace std;
constexpr int N = 1e2 + 5;
const double eps = 1e-6;

inline int read(){
    register char ch = getchar();
    register int x = 0;
    register bool f = 0;
    while(!isdigit(ch)) f |= (ch == '-') , ch = getchar();
    while(isdigit(ch)) x = (x << 3) + (x << 1) + (ch ^ 48) , ch = getchar();
    return f ? -x : x;
}

int n;

double a[N][N];

inline int Gauss(){
    bool flag = 0;

    int nowline = 1;

    for(register int i = 1 ; i <= n ; ++ i) {

        for(register int j = i ; j <= n ; ++ j)
            if(fabs(a[j][i]) > eps) {
                swap(a[i] , a[j]);
                break;
            }

        if(fabs(a[i][i]) < eps) {
            flag = 1;
            continue;
        }

        //for(register int j = 1 ; j <= n + 1 ; ++ j) swap(a[newline][j] , a[nowline][j]);
        for(register int j = n + 1; j >= i ; -- j) a[i][j] /= a[i][i];

        for(register int j = i + 1 ; j <= n ; ++ j)
            for(register int k = n + 1 ; k >= i ; -- k)
                a[j][k] -= a[i][k] * a[j][i];

        //++ nowline;
    }

    if(flag) {
        for(register int i = 1 ; i <= n ; ++ i){
            bool yg = 0;
            for(register int j = 1 ; j <= n ; ++ j) {
                if(a[i][j] != 0) {
                    yg = 1;
                    break;
                }
            }
            if(yg) continue;

            if(fabs(a[i][n + 1]) > eps) return -1;      
        }       

        return 0;
    }

    for(register int i = n ; i ; -- i)
        for(register int j = i + 1 ; j <= n ; ++ j)
            a[i][n + 1] -= a[j][n + 1] * a[i][j];

    return 1;
}

int main(){
    n = read();

    for(register int i = 1 ; i <= n ; ++ i)
        for(register int j = 1 ; j <= n + 1 ; ++ j)
            a[i][j] = read();

    int backin = Gauss();

    if(backin == 1)
        for(register int i = 1 ; i <= n ; ++ i)
            printf("x%d=%.2f\n" , i , a[i][n + 1]);

    else printf("%d" , backin); 
    return 0;
}