IF's

// y = a/150*(x-b)^2+c;
struct Parabola {
    int a;
    int b;
    int c;
    Parabola():a(0),b(0),c(0){}
    Parabola(int a, int b, int c):a(a),b(b),c(c){}
    Parabola(Parabola const& p):a(p.a),b(p.b),c(p.c){}
};
struct Record {
    Parabola para;
    int      count;
    Record():para(),count(0){}
    Record(int a, int b, int c, int cnt):para(a,b,c),count(cnt){}
};
struct RecordCmp {
    inline bool operator()(Record const& a, Record const& b) {
        return a.count>b.count;
    }
};
std::vector<Parabola> detectParabolas( cv::Mat const& img,
                                       int minA=-1,
                                       int maxA=-1,
                                       int minB=-1,
                                       int maxB=-1,
                                       int minC=-1,
                                       int maxC=-1 )
{
    cv::Mat edges;
    // cv::imshow("debug", img);
    // cv::waitKey(3000);
    cv::Canny( img, edges, 50, 150 );
    cv::Mat_<uint8_t> img_(edges);
    // cv::imshow("debug", edges);
    // cv::waitKey(3000);
    int ***acc = 0;

    if(minA < 0)
        minA = 1;
    if(minB < 0)
        minB = img.cols/4;
    if(minC < 0)
        minC = img.rows/4;
    if(maxA < 0)
        maxA = 60;
    if(maxB < 0)
        maxB = img.cols/2+img.cols/4;
    if(maxC < 0)
        maxC = img.rows;

    acc = new int**[maxA+1];
    for(int i=0; i<maxA+1; ++i) {
        acc[i] = new int*[maxB+1];
        for(int j=0; j<maxB+1; ++j) {
            acc[i][j] = new int[maxC+1];
            for(int k=minC; k<maxC+1; ++k) {
                acc[i][j][k]=0;
            }
        }
    }

    printf("calculating ...\n");
    int percent=0;
    for(int y=0; y<img.rows; ++y) {
        for(int x=0; x<img.cols; ++x) {
            if(img_(y,x)) {
                for(int a=minA; a<=maxA; ++a){
                    for(int b=minB; b<maxB; ++b) {
                        int c=y+a*(x-b)*(x-b)/150;
                        if(c>=minC && c<=maxC) {
                            ++acc[a][b][c];
                        }
                    }
                }
            }
        }
        int p=int(round(double(y)/img.rows*100.));
        if(p!=percent) {
            percent = p;
            printf("> %02d%%\n", percent);
        }
    }
    printf("done!\n");

    sizedpq<Record, RecordCmp> pq(3);
    for(int i=minA; i<=maxA; ++i) {
        for(int j=minB; j<=maxB; ++j) {
            for(int k=minC; k<=maxC; ++k) {
                pq.insert(Record(-i,j,k, acc[i][j][k]));
            }
        }
    }

    for(int i=0; i<=maxA; ++i) {
        for(int j=0; j<=maxB; ++j) {
            delete[] acc[i][j];
        }
        delete[] acc[i];
    }
    delete[] acc;

    std::vector<Parabola> res;
    for(int i=0; i<3; ++i) {
        res.push_back(pq[i].para);
    }
    return res;
}