[LeetCode] 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.
【thought】Use two layers of loop to solve it.Do not start the second loop from points.begin() but item1+1 (item1 is the current item of the first loop).We can avoid accessing any 2 duplicated points which could compose one straight line with this method.Any better solution?If any there,pls tell me.Thanks.
1 #include <iostream> 2 #include <algorithm> 3 #include <unordered_map> 4 #include <vector> 5 #include <limits> 6 7 using namespace std; 8 9 /** 10 * Definition for a point. 11 * struct Point { 12 * int x; 13 * int y; 14 * Point() : x(0), y(0) {} 15 * Point(int a, int b) : x(a), y(b) {} 16 * }; 17 */ 18 19 bool typeisless(const Point &data1,const Point &data2){ 20 return data1.x < data2.x; 21 } 22 23 class Solution { 24 public: 25 26 int maxPoints(vector<Point> &points) { 27 if(points.size()==0) return 0; 28 29 int last_x = (points.begin()->x) - 1; 30 int maxnum = INT_MIN,curnum = 0; 31 std::sort(points.begin(),points.end(),typeisless); 32 for(vector<Point>::iterator iter = points.begin(); 33 iter != points.end();++iter){ 34 if(iter->x == last_x){ 35 ++curnum; 36 }else{ 37 last_x = iter->x; 38 curnum = 1; 39 } 40 41 maxnum = maxnum<curnum?curnum:maxnum; 42 } 43 44 unordered_map<double,int> count_map; 45 count_map.insert(pair<double,int>(0.0,0)); 46 47 for(vector<Point>::iterator iter1 = points.begin(); 48 iter1 != points.end();++iter1){ 49 count_map.clear(); 50 int samepointnum = 0; 51 52 for(vector<Point>::iterator iter2 = iter1 + 1; 53 iter2 != points.end();++iter2){ 54 55 if(iter2->x == iter1->x && iter2->y == iter1->y){ 56 ++samepointnum;continue; 57 }else if(iter2->x == iter1->x) 58 continue; 59 else{ 60 double dslope = (static_cast<double>(iter2->y - iter1->y))/ 61 (static_cast<double>(iter2->x - iter1->x)); 62 if(count_map.find(dslope) != count_map.end()) ++count_map[dslope]; 63 else{ 64 count_map[dslope] = 1; 65 ++count_map[dslope]; 66 } 67 } 68 } 69 70 for(unordered_map<double,int>::iterator iter=count_map.begin(); 71 iter!=count_map.end();++iter){ 72 if(iter->second + samepointnum > maxnum){ 73 maxnum = iter->second + samepointnum; 74 } 75 } 76 } 77 78 return maxnum; 79 } 80 };
