洛谷.3389.[模板]高斯消元法

Posted 2020-10-24 SovietPower

题目链接

#include <cmath>
#include <cstdio>
#include <algorithm>
const int N=105;
const double eps=1e-10;

int n;
inline bool bigger(double a,double b) {return std::fabs(a)>std::fabs(b);}
inline bool cmp(double a) {return std::fabs(a)>eps;}
struct Gauss
{
    double f[N][N],ans[N];
    void Init()
    {
        for(int i=1; i<=n; ++i)
            for(int j=1; j<=n+1; ++j)
                scanf("%lf",&f[i][j]);
    }
    bool Solve()
    {
        for(int j=1; j<=n; ++j)
        {
            int mxrow=j;
            for(int i=j+1; i<=n; ++i)
                if(bigger(f[i][j],f[mxrow][j])) mxrow=i;
            if(mxrow!=j) std::swap(f[j],f[mxrow]);
//              for(int i=1; i<=n+1; ++i)
//                  std::swap(f[j][i],f[mxrow][i]);
            for (int i=j+1; i<=n; ++i)
                if(cmp(f[i][j]))
                {
                    double t=f[i][j]/f[j][j];
                    for(int k=1; k<=n+1; ++k)
                        f[i][k]-=f[j][k]*t;
                }
        }
        for(int i=n; i; --i)
        {
            if(!cmp(f[i][i])) return 0;
            for(int j=i+1; j<=n; ++j)
                f[i][n+1]-=f[i][j]*ans[j];
            ans[i]=f[i][n+1]/f[i][i];
        }
        return 1;
    }
    void Print()
    {
        for(int i=1; i<=n; ++i) printf("%.2lf\n",ans[i]);
    }
}g;

int main()
{
    scanf("%d",&n);
    g.Init();
    if(g.Solve()) g.Print();
    else printf("No Solution");
    return 0;
}