Gaussian Elimination

/*
 * Algorithm: Gaussian Elimination
 * Complexity : O( N^3 )
 */
typedef vector<double> VD;
/* indexin 0 base */
/* return 1 if unique sol ,0 if no sol , INF if multiple sol */
long Gauss( vector<VD> A,vector< double> &Ans )
{
    long Row = (long)A.size();
    long Col = (long)A[0].size() - 1;
    vector<long> Where( Col,-1 );
    long r,c,i,j;
    for( c=0,r=0;c<Col && r<Row;c++ ){
        long sel = r;
        for( i=r;i<Row;i++ ){
            if( fabs( A[i][c] ) > fabs( A[sel][c] ) ) sel = i;
        }
        if( fabs( A[sel][c] ) < EPS ) continue ;
        swap( A[sel] ,A[r] ) ;
        Where[c] = r;
        for( i=0;i<Row;i++ ){
            if( i==r ) continue;
            double CON = A[i][c] / A[r][c] ;
            for( j=c;j<=Col;j++ ) A[i][j] -= A[r][j]*CON;
        }
        r++;
    }
    Ans.assign( Col,0 ) ;
    for( i=0;i<Col;i++ ){
        if( Where[i]==-1 ) continue;
        Ans[i] = A[Where[i]][Col] / A[Where[i]][i];
    }

    for( i=0;i<Row;i++ ){
        double Where = 0;
        for( j=0;j<Col;j++ ) Where += Ans[j] * A[i][j];
        /* Found a row which hs all zero co-eff */
        if( fabs( Where - A[i][Col] ) > EPS ){
            return 0;
        }
    }
    for( i=0;i<Col;i++ ){
        if( Where[i] == -1 ){
            return INF ;
        }
    }
    return 1 ;
}