整数高斯消元模板

#include<cstdio>
#include<algorithm>
#include<cstdlib>
using namespace std;
#define MAXN 400
int a[MAXN+10][MAXN+10],x[MAXN+10],n,m,row;
template<class T>
void Read(T &x){
    char c;
    bool f=0;
    while(c=getchar(),c!=EOF){
        if(c=='-')
            f=1;
        if(c>='0'&&c<='9'){
            x=c-'0';
            while(c=getchar(),c>='0'&&c<='9')
                x=x*10+c-'0';
            ungetc(c,stdin);
            if(f)
                x=-x;
            return;
        }
    }
}
void read(){
    Read(n),Read(m);
    int i,j;
    for(i=1;i<=n;i++)
        for(j=1;j<=m+1;j++)
            Read(a[i][j]);
}
int gcd(int a,int b){
    int t;
    while(b){
        t=a%b;
        a=b;
        b=t;
    }
    return a;
}
void gaussian_elimination(){
    int col,i,mxr,j,lcm;
    for(row=col=1;row<=n&&col<=m;row++,col++){
        mxr=row;
        for(i=row+1;i<=n;i++)
            if(abs(a[i][col])>abs(a[mxr][col]))
                mxr=i;
        if(mxr!=row)
            swap(a[mxr],a[row]);
        if(!a[row][col]){
            row--;
            continue;
        }
        for(i=row+1;i<=n;i++)
            if(a[i][col]){
                int t1=lcm/a[i][col],t2=lcm/a[row][col];
                lcm=a[row][col]/gcd(a[row][col],a[i][col])*a[i][col];
                for(j=m+1;j;j--)
                    a[i][j]=a[i][j]*t1-a[row][j]*t2;
            }
    }
    row--;
}
void find_ans(){
    if(row==m){
        int i,j;
        for(i=n;i;i--){
            for(j=i+1;j<=m;j++)
                a[i][m+1]-=a[i][j]*x[j];
            x[i]=a[i][m+1]/a[i][i];
            printf("x%d=%d\n",i,x[i]);
        }
    }
}
int main()
{
    read();
    gaussian_elimination();
    find_ans();
}