Max Points on a Line

Given n points on a 2D plane, find the maximum number of points that lie on the same straight line.

参考：http://blog.csdn.net/doc_sgl/article/details/17103427

AC的代码：

#include<iostream>

#include<map>

#include<vector>

#include<set>

#include<unordered_map>

#include<climits>

using namespace std;



struct Point

{

    int x;

    int y;

    Point():x(0),y(0) {}

    Point(int a,int b):x(a),y(b) {}

};



class Solution {

public:

    int maxPoints(vector<Point> &points) {

        // IMPORTANT: Please reset any member data you declared, as

        // the same Solution instance will be reused for each test case.

        unordered_map<float,int> mp;

        int maxNum = 0;

        for(int i = 0; i < points.size(); i++)

        {

            mp.clear();

            mp[INT_MIN] = 0;

            int duplicate = 1;

            for(int j = 0; j < points.size(); j++)

            {

                if(j == i) continue;

                if(points[i].x == points[j].x && points[i].y == points[j].y)

                {

                    duplicate++;

                    continue;

                }

                float k = points[i].x == points[j].x ? INT_MAX : (float)(points[j].y - points[i].y)/(points[j].x - points[i].x);

                mp[k]++;

            }

            unordered_map<float, int>::iterator it = mp.begin();

            for(; it != mp.end(); it++)

                if(it->second + duplicate > maxNum)

                    maxNum = it->second + duplicate;

        }

        return maxNum;

    }

};



int main()

{

    Solution s;

    vector<Point> pp= {Point(0,0),Point(0,0),Point(3,10),Point(0,2),Point(0,2),Point(3,10)};

    cout<<s.maxPoints(pp)<<endl;

}

超时的代码：

#include<iostream>

#include<map>

#include<vector>

#include<set>

using namespace std;



struct Point

{

    int x;

    int y;

    Point():x(0),y(0) {}

    Point(int a,int b):x(a),y(b) {}

};

struct Line

{

    double k;

    double t;

    Line(double a,double b):k(a),t(b) {}

};

bool operator==(const Point &a,const Point &b)

{

    return a.x==b.x&&a.y==b.y;

}

bool operator<(const Point &a,const Point &b)

{

    return a.x==b.x?a.y<b.y:a.x<b.x;

}

bool operator==(const Line &a,const Line &b)

{

    return a.k==b.k&&a.t==b.t;

}

bool operator<(const Line &a,const Line &b)

{

    return a.k==b.k?a.t<b.t:a.k<b.k;

}

class Solution

{

public:

    int maxPoints(vector<Point> &points)

    {

        if(points.empty()||points.size()==1)

            return points.size();

        map<Line,set<Point> > mp;

        int i,j;

        int count=0;

        for(i=0; i<(int)points.size()-1; i++)

        {

            for(j=i+1; j<(int)points.size(); j++)

            {

                Point x=points[i];

                Point y=points[j];

                double k;

                double t;

                if(x.x==y.x)

                {

                    k=1e20;

                    t=x.x;

                }

                else

                {

                    k=(y.y-x.y)/(y.x-x.x);

                    t=x.y-x.x*k;

                }

                mp[{k,t}].insert(x);

                mp[{k,t}].insert(y);

            }

        }

        auto start=mp.begin();

        while(start!=mp.end())

        {

            cout<<start->first.k<<" "<<start->first.t<<" "<<start->second.size()<<endl;

            set<Point> st=start->second;

            multiset<Point> mul(points.begin(),points.end());

            auto it=st.begin();

            int dup=0;

            while(it!=st.end())

            {

                dup+=mul.count(*it)-1;

                it++;

            }

            if(count<(int)st.size()+dup)

                count=st.size()+dup;

            start++;

        }

        return count;

    }

};



int main()

{

    Solution s;

    vector<Point> pp= {Point(0,0),Point(0,0),Point(3,10),Point(0,2),Point(0,2),Point(3,10)};

    cout<<s.maxPoints(pp)<<endl;

}